Unfortunately, as far as I know, the midi standard does not support that.. :( there's on & off messages, but the on message does not provide information about how long a note is. (Presumably because midi can be played live as well, of course.)
It's possible to fade out at a 1/4th note, but not if you're doing things like kickrolls, so it's a bit difficult. The best way to do it right now is to make the notes a bit shorter and rely on the ADSR.
