Just replace the front lever---you no longer need the front shifter with your BBSHD.
I love my Avid BB7 disc brakes better than my Hydraulics---simpler and they work great.
I only have the cutoff lever on my front brake. I use it to shift also. Tap the brake and shift---it is easy once you get used to it.
Another option is just click to zero on your assist and then shift. I shift rarely with my e bike. (BBS02 on a hard tail Mountain bike).
Good luck