Like I said, it still doesn't work as well as a locked diff., but it'll help with what he's got. And Yamaha is not the only mfg. with locking front diffs, In fact, Suzuki's is supposed to work the best because it does not require the front tires to move in order to engage (like when you get stuck in 2wd).

 

I've tried the brake trick with my 300 Honda but I can never get it to work quite as well as I can in a pickup or bronco. My old ford had an open front end and with a little finesse on the brake it would lock the front up surprisingly well.