I'm not sure how fruitful a path that is. (I'm also completely uneducated as regards MMS -- Sprint's implementation has always been so abysmal, and I've always had phones that could do email, so... who cares?) It sounds like you've got way more of a feel for MMS than I do, but these Frankenstein's Monster GSM-build-on-a-CDMA-phone devices are definitely put together in a very strange way, and what works on regular Android devices might not be all that useful. Fair warning.
That said, I would imagine the best starting points are: hamagc got sending working, in
this post. (I tried his settings, I wasn't able to actually send audio or video, but the mms gateway (?) worked, which seems like a big hurdle.)
The people over at xda developers have been putting some work in to getting MMS working on Sprint on the Vogue-Android port,
here, as well as in other threads. Their work almost certainly won't translate to our devices, as they use a different RIL, but some lurking over there could figure out where the issues are and what needs to be modified in the MMS app to get things up and running. There's also a lot of boards about native android devices, and some hacking in the mms app going on there, which might also be of use -- I'm not sure.
I won't discourage you from checking out how it's done on real CDMA Android devices, because that could be quite valuable... but I think whatever you find from them will have to be mangled pretty heavily to fit into our devices.
Good luck.