If you decide to implement this in an existing or new bitcoinj based wallet, then I'm happy to give you pointers on how to do it. Making one-off, cross platform app specific wallets is pretty easy these days. For 2-of-3 dispute mediation transactions they'd start out being kind of specialist so asking people to move money from their general spending wallet into dispute mediation app isn't unthinkable. Eventually general purpose wallets would integrate protocol, UI ideas and maybe code.
At least, that's how I'd do it.