I do that same thing. I used midi "drumtrax" which may not still be on
the market. A better solution, IMO, is to find drum wav files of
grooves. Most of them allow you the vary the tempo without changing
the pitch. That's what I use now...forget the product and I am not on
my Daw now. I'll check back later...bought it on ebay...search for
drum tracks.

Tom Paul