Hmm.. The other way I know to increase ero is by : 1. Getting captured in the deserted base and purposefully getting toyed with by mystra (Don't overstay or you'll get a bad end)
Or
2. Doing dance's in the desert sunshine town brothel
It'd be nice to have a way to bulk-work at Gentlemen's Club. As is it's already a fixed stamina cost with no per-day limit so with a bulk option it'd be possible to train it up after doing res training the normal way.