What I do can be applied to percussion, but I do this with other instruments and instrument combinations. Note that what I describe below can be done only in an improvisation session, not in the writing process, but maybe some ideas can be generalized. My synthesizer, Yamaha Motif S90ES, has a fantastic feature called arpeggios. On the first sight this may look as a tool for non-professionals, but wait. Imagine a few thousand phrases, meticulously prepared and performed by real performers on real instruments and instrument groups. Each phrase contains 10-20 notes or more and is designed so that it can be applied in a loop. Now, you choose a phrase (arpeggio), play some accord, and the phrase is repeatedly played using the notes you have chosen (and maybe some additional notes); you can change this on the fly and simultaneously play something else using the same and/or additional keyboard. Then you can edit the results using the MIDI result of this session.
This is somewhat simplified picture; there are ways to create new arpeggio phrases, to change the tempo or swing of the arpeggios, to make them more or less sensitive to the velocity of the pressed notes, to apply arpeggios for different instruments etc. As far as I know, in Yamaha they strive to develop this feature, and I heard of instruments containing 6000 arpeggios, and even of the possibility to play 2 arpeggios simultaneously. I am extensively experimenting with this feature now, but so far I succeed to create only one full piece using it - this is "Small Fantastic Dance" presented in my profile here.
