You can also use the draw tool in prv mode to manaully draw in velocity values. The effectiveness of this will depend upon the sophistication of the drum software you are using, but I find it works quite well with SD, BFD and such.

I have over 300 bars of midi-drum hits so most of the solutions do not help me, thanks anyway.
 
Groove Quantize is the way to go I think, but I can only get it to humanize the velocity and not the start-times.
 
In the good old days this used to be so much more easier (R.I.P. Pro Audio 9).