One of the glorious tidbits from the Barkers' ball python book (http://www.amazon.com/Ball-Pythons-H.../dp/0978541103) is that they do not, in fact, ejaculate. At least, not in the same way mammals do -- their sperm swims through channels along the hemipene he's using on their own power. So, can a male release without being inside a female? Sure. I can think of no physical reason why he couldn't.
Hemipenial casts pop out whenever a hemipenis is everted. If there's enough material to have formed a cast, it's coming out with the pene.
Hopefully of all my wording made sense.