i just wonder, i think it’s pretty possible and isn’t too hard. i recently have done some scratcher ensemble for Reaktor 3, and the result is great. but i have to record it into wav in Reaktor before using. and i don’t want to use Reaktor as vst plugin, it eats too much of cpu time.
you can check my scratcher (and use it if you like it), but the main idea is make some “instrument envelope” as mentioned already, and make there “scratch position”, and maybe a couple of another parameters like “inertia” and etc. i think could be really cool.
http://tsd.urbankillah.com/scratch.gif
http://tsd.urbankillah.com/scratcher.rar (winrar 3 needed to extract)