Chas
You can set up a volume pedal to effect anything you want. The Bass (or anything else ) could be covered by Dynamic Arranger touch control so you can have two types of volume control. Think of using your B3 being upgraded with pedal for lower manuel/bass pedals and having velocity sensativity volume control on your upper manuel.

Lots of editing choices available on the BK9.
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer