I have not played the co-op here so I am going off a few reviews. Even if you could twist VC3 multiplayer to your own ends (often far nicer than having to make your own network code) I doubt it would be an easy hack to pull off, indeed I would probably look to backporting maps and methods to the earlier title before I did. As VC3 seems to lack multiplayer of any kind you do not have that option either so you get to have some real fun.
The VC2 co-op seems to amount to "import characters and take turns" so you do have some options. My first thoughts would be to kick it kind of PC style with a kaillera type thing, maybe backed with some cheats to allow character imports (if indeed it is different enough to warrant the effort -- the progression seems to be more story/fixed for this one so it might not be). You would want to find some way to transmit a screen around and get commands back over a network. Not great for active games but turn based should be OK. I would probably use the TV out options of a PSP rather than network for screen grabs and then network for the controls before playing with a soldering iron (though it is a good option).
if the other option still is "just pass the controller" then you might have a harder sell if you need to put a team together.