[Rwp] a midi challenge for reaper sperts

[Chris Belle]

Ok here's one for ya.
I want to map a drum note to several other notes for easier more 
expressive playing, like doing a drum roll.
If I were building my own sfz library, it would be easy but I want to do 
this for external midi or other soft synths.
Now I have some partial success by using one of the midi mappers in the 
js plugs,
midi router/transpose where I put the drum kit on two octaves so I get 
two keys for each note in different octaves.
I could build something up with multiple plugs, but I am imagining there 
is a easier way to do this,
I saw one thing which had mapping files you could load, but don't know 
how to create a mapping file for it, but with all the jiggery pokery 
things you can do in reaper, I saw every kind of mapping thing 
imaginable in there, surely this is not too hard to do.
Has anyone done this before, and which plug is the easiest to do it with?