Quote johnny h:
You can get a midi retrofit from Kenton - I think its about £300 so not exactly cheap but Kenton are top quality. It even lets you externally control the filter cutoff.
Not having MIDI does tend to improve your timing a lot ... but if you are recording filter sweeps and the like its extremely useful.
A footswitch and expression pedal are cheaper.
Besides, there's something liberating about not being able to rely on MIDI for tight timing or whatever. It's an instrument that's meant to be played, so play it, methinks.