I believe the final distribution step requires a Mac, even if you are talking about an Enterprise distribution certificate and not an Apple Store certificate. I have not gone through the process for an Enterprise app, but I do recall reading that there is a handshake process that takes place with Apple even for an Enterprise app, and my suspicion is that it is simply a variation of the process required for submission to a store -- which requires a Mac (there's some special utility inside of Xcode that does the magic).
It's possible someone may have figured out a way around this, but every attempt I have seen is that it ultimately requires a Mac. There are people that will submit apps to the Apple Store on your behalf, using their Mac, but I'm not sure how well that would work with an Enterprise distribution, you might be giving out some information you don't want them to have.
Apple keeps a very tight rein on their developer program and distribution of iOS apps. We are not able to go around that system and we are not in a position to attempt to do so. It would not bode will for our relationship with Apple.
