I actually just did this a few hours ago for myself. I double nutted it. Worked like a charm.
I had to take both studs out of the front motor mount completely. I don't plan on replacing them (they don't fit around my bike's thicker front tube - Yea, I've got the universal mount option but it's useless for me... not enough space.) My bike's "vee" is so tight that if I do anything with the front motor mount at all then the motor won't fit at all (the top of the spark plug boot is already rubbing on the top tube (ow!)
So, my rear engine mount gets tightened very tight while the motor is in the lowest point possible in the vee and the front motor mount has a friction fit (the mount's "crotch" hangs on) on the thicker variety front tube... I've got a big u-bolt pushing down on the front motor mount to keep the motor from rising and the front motor mount crotch hanging on preventing sideways movement - HOPEFULLY (fingers crossed that the motor will be stable this way... we'll see...)
If that doesn't work I guess I'll either have to buy a new bike or take the old one into a weld shop for mods...