Following up from the preceding post on obscene compounds starting with verbs, I'm linking to the slang.gr entry for the use of γαμο- as a prefix, for two reasons.
The first reason is, the entry identifies other instances in the slang.gr dictionary of /ɣam/ as the first part of a compound, and it highlights its linguistic oddity. The first oddity is, these compounds are unusual as forming a verb-initial compound class. Verb–noun compounds in Modern Greek are probably as productive as the Early Modern English equivalent John Cowan pointed to in comments (tosspot, scofflaw), but they're still not all that common, and they're restricted to the colloquial register.
The second oddity is that /ɣam/ can be used as a productive expletive attaching to any noun, without actually referring to the act of copulation. As in γαμοσταυρόλεξο "fucking crossword".
That's sort of news to me, but slang.gr does not lie. My ossified Greek is familiar with σκατο- "shitty" in that usage instead (like German Scheiß-). I'm guessing this use of is γαμο- is recent, and is transparently a borrowing from English—just like the expletive I actually have heard recently, γαμημένος "fucked".
Hence the incredulous slogan once Greece started to look likely to win the 2004 European UEFA championship: σήκωσέ το το γαμημένο, δεν μπορώ, δεν μπορώ να περιμένω, "lift it up, the fucking thing [the trophy], I can't wait any more". Subsequently coopted by the mass media, where it was necessarily bowdlerised to τιμημένο, "the honoured thing".
But then, slang calques, as the Balkans richly attests: today it's English, yesterday it was other hegemoniacal languages. You don't think τρώω ξύλο "eat wood" for "get beaten up" comes straight from Homer, do you?
I'd add that a quotative use of γαμώ (as in, the word used in a compound actually quotes its use in full as a verb in a phrase) is possible some times, as vikar posits in his post on γαμο-, and indeed has been conventional in spelling. Compounds like γαμωσταυρίδι "I-fuck-cross-thing = blasphemous swearing" is a reference to the oath γαμώ το σταυρό σου "I fuck your cross", and can be interpreted as the embedded quotation «γαμώ-[το-]σταυρ-»ίδι. In that case, the omega ("I-fuck-cross-thing") can be justified, it really is an inflection. That kind of quotation in compound does come up elsewhere in slang, as in ωχαδελφισμός "'Come-On-Brother'-ism = systematic indifference".
(There was a pretty decent English Wikipedia article on ωχαδελφισμός once, but it's been whittled down. Yes, it's not encyclopaedic, but it is lexicological...)
You could argue the same for γαμαοδέρνουλας, as I did in passing: that γαμαο- is quoting the first verb of γαμάω και δέρνω, so it should be spelled like an inflected verb. But that's highly unusual for Greek in general—and γαμαωδέρνουλας "Lord Master 'I-Fuck-and-Bash'" looks even stranger than γαμαοδέρνουλας "Lord Master Fuck-and-Bash" already looks.
But internal inflection is still a barrier to a compound being linguistically acceptable: it violates the sense of the compound being a single linguistic unit. French-inspired compounds like παιδιά-θαύματα "child[ren]-wonders", λέξεις-κλειδιά "key-words", like English singers-cum-songwriters, don't comply with that notion, admittedly. Τhen again, without the linking /-o-/, and precisely because the two halves inflect independently, they shouldn't really be considered compounds at all. They're more a coordinated phrase, minus the and coordinator.
The test for whether to use an omega or an omicron in such compounds as γαμαοδέρνουλας or γαμοσπέρνω, as vikar rightly says, is whether you could conceivably have another inflection on the first half of the compound. Can you use expressions like χεσε-μεσ-όβιος (imperative), έγραψες-ατζής (aorist), κλαφ-τα-Χαραλαμπ-άκιας (imperative)? Well, nothing's really impossible in language, but only the last one sounds plausible to me. (I could argue why, but I've detoured enough in this post already.)
The other reason for this post is that vikar has given me a shout out in his own post. I am very, very far from being above that kind of thing.
I return the favour by retracting my definition of slang.gr, as the Greek equivalent of Urban Dictionary. The Urban Dictionary *wishes* it was both as entertaining and as erudite as slang.gr. Seriously, for all the shaggy dog stories and obscenity and made up words over there, slang.gr has some serious linguistic analysis going on. There are reasons why slang.gr has done better than Urban Dictionary: its format encourages longer definitions, and it has a much smaller and more focussed community behind it. It's sort of a blog vs a microblog approach to online lexicography.