The gold standard would be to play bass on the pedals, organ-style. Of course this takes a lot of training and skill. Lowrey organs make this approach a little easier by letting the players override the arranger for a couple of measures, and then the arranger automatically resumes control of the bass pattern.

Another approach would be to record ONLY the bass line (or part of it) as a single track MIDI, and then play the rest of the arrangement over it. This would require an arranger capable of playing MIDI and style chord recognition at the same time. Most cannot do this. You might be able to do it with multipads.

A third approach might be to pre-record all of the chord changes in a chord sequencer, and play the bass and melody "live." Good discussion!