An interesting point would be, what is the earliest known usage of a version of this rhyme?

If we know when (as in "I'm just a...") Gigalo was in contemporary usage that might shed some light on things. Presumably the idea of a "hired male dancing partner/escort" led to the sexual conotation, but the etymology still points ultimately to gigue, which I think is where the smart money is.

Gigalo (man) I'd always assumed was an american word - Do we know anything more about the origins of the british Jackalo?

cheers,
Jon