Sorry, can’t be done - this would need to be a native solution.
Only workaround I can think of is to run something like a small VST/external program which is capable of hosting the MIDI plugin, and then using virtual MIDI cables to route the notes from Renoise into that plugin, and then send the result back to (specific) instrument(s) in Renoise. But you’d probably suffer from the timing issues that MIDI has (take a few pills against seasickness before composing!)
I’ve caught the ctrlr bug pretty heavily, It’s a damn shame that vsts inside of renoise can not send MIDI out natively. How far off is this capability? I tried the energyXT solution - kinda lame workaround… sure it does the trick but lame. Renoise should be capable of this w/o help from other apps.