I used "reajs" from the free set of plugins from REAPER. See pic
Once installed, add the reajs vst before the Note Dispatcher, double click the reajs module and select LOAD>MIDI>midi_note_hold
The way Ive got it set up at the moment, reajs has to be the focused module.
The sequence players have to be setup with....
Start Mode---on every note on
Stop Mode---on last note off
Its not perfect as I havent figured out how to stop the sequences once started but it does stop the previous sequence when playing the next one and I have only tried it using the round robin setting.
There maybe other midi vst's that can be used like this but this was the first I tried.
You could give it a try and see what you think
