I don't think a realistic roll is hard to achieve at all with manual programming. Especially if you are mindful of the mechanics of a fast snare roll. You can tell when a drummer is doing solid alternating hits and when they are bouncing the stick a little - you should be able to hear such things in programmed drums too.
I often do rolls that try and emulate the bouncing stick effect. Instead of alternating right / left hits, I do 2 or sometimes more hits in a row for each hand, alternating, that quickly drop in velocity. Keeping everything below 60-70 and sometimes even below 40 for the "ghost notes" or whatever you want to call them, makes things sound alot more real. I also use rhythmic spikes in the velocity to sort of simulate the natural tendancy for a drummer to do so.
For example, I might start a roll with a right hand hit at around 70-80 velocity, then draw another hit for the right hand right after that one (a 32nd note maybe) and have the velocity at around 40. Then a hit from the left hand at around 60 and a second at 40, so on and so forth. I've built up some pretty realistic rolls by doing that. You can draw in a whole measure of a snare roll in just a minute or two, tweaking things a little if it sounds unnatural.
I really think the best sounding hits in DFHS are the light ones. Lower velocity and more compression during mixing takes the cake for realism. At least in my opinion.
