Paul,
I've used the arranger in arranger mode - but with a lot of the acc turned off - with both a guitar player and a bass player ... even with a drummer while the arranger played the bass part ... they have to LISTEN, but it can be done ...
if he is as good a musician as you are you shouldn't have a problem ... make sure there is a monitor close by ...
Best wishes, and let us know how it works out ...