Basically all a drum roll is a sped up sequence of successive hits at usually an increasing velocity.....
try putting 16 notes on the drum roll view then from the first note use the lightest velocity then increase it lik 1 increment or so thru each note till the last note is the hardest.....then you can experiment with the time signature until you get it how you want....that's what I would try doing, I only did this using software...on fruity loops, fruity loops has a key sequence...ctr L something and it paints a roll....it sounds like a machine gun...itz cheesy but you can work with it to try and make it sound real....but it won't fool too many people though....