There might be a way to bypass chord changes... record the part as a drum part. Send it out as MIDI and then back in to the same board on a different MIDI channel mapped to a voice like Lower or Right 2. Another option: if you're bypassing chord changes then you're talking about a MIDI sequence so you don't need an arranger per se. You could add a Yamaha QY700 outboard hardware sequencer, or even a Motif XF Rack module. Maybe the best of all worlds...?

One last thought (because ya know, you need another Roland arranger for your stable ;-) On the E-A7, the multipads ALWAYS transpose but they are still active while an SMF is playing. You can copy style parts, including the Bass part, to the multipads and then play over the SMF. E-A7 is the only Roland with multipads, and the only one that can use the arranger and SMF player at the same time. For the record I agree 100% that Roland should have included a "Bypass" or no transpose parameter, would have made things much easier. FWIW.