You can likely do this from your e-drum kit (my TD-4 supports such a feature). If not, there is a 20$ (demo available) program that you can use to do this easily:
http://www.midikarval.net/MidiMapper.html
However, with some swapping and mixing around, you can probably achieve what you want using some of the free tools here:
http://freemusicsoftware.org/category/f ... ent-filter
What you want to use is "Note on velocity" with your rimshot note, replacing the low input and high input from a range of 0 - 90 with the note for cross-stick instead. I haven't done it with the free tools myself, but if I figure it out in the future I will explain things a little better
