yep, there's some pretty n00bish stuff going on here, but none of it from the original poster
seriously people, if you don't have a clue...don't post. "Sometimes its better to be thought a fool, then to open your mouth and remove all doubt"
back on topic though
although I have no idea why you'd need it, it actually wouldn't be too hard. 'tuning' the stock system to handle another channel isn't going to happen. doing it remotely would be virtually impossible (you'd need to convert to hobby grade electronics, and to effectively control it, a many hundred dollar system at that).
BUT, you might be able to make something to effectively disengage the driveshaft, or one of the front dogbones. heck, if you've got an evo, get some hot racing alloy front knuckles. then the only tool you need to pull a front dogbone is the lug wrench. pull of the wheel, unscrew the cap over the bearings, slide the stub and dogbone out, replace stub, replace cap, replace wheel. done! (and you'd only have to do it to one side, as long as the front diff isn't locked, it'll just slip and act as RWD)
the problem is, you wouldn't see the performance increase from switching it to 2WD. because all the gears would still be there, and still be turning (unless you removed the pinion gear, and BOTH dogbones, in which case you might as well remove the front diff too....), and still be eating power through friction, but you'd just have less traction.