90% of all automatic transmissions with paddle or sequential-style stick shifting suck ass. even Ferrari's. that thing is so F'n slow. same with the bmw (NOT the SMG, which is a manual trans) and the lexus, and all the others (except audi, the got a good one).
there is no modification you could make to a stock manual trans to 'add' paddles, at least not effectively. it would be damn near impossible to have a mechanical linkage from paddles to the trans, so it needs to be electronic. anything in kit fashion is going to be slow as shit.
if you are dead set on this dont spare any expense. go all out and get a sequential dog box so you can quit with the silly clutch work. whats the fn point in sequential box if you still have to use the clutch?