My SMB has one clip to attach to my BCD. I could keep a finger spool with me in my BCD pocket, but I worry about the spool becoming tangled up before or while trying to deploy the SMB. Scenario: Untangle finger spool and wrap up again, attach SMB to finger spool, unroll SMB, manually inflate SMB (reg out of mouth, partially inflate SMB, purge reg, breath, reg out of mouth again, inflate SMB some more, purge reg, and breath), deploy SMB, then surface.
Jewels, I am somewhat in the same boat as you with the SMB (wish I would have another option other than manual inflation, and an overpressure relief), but have played a little to get it to work (although I still want to do more practice before my next trip).
1st, attach the smb to a finger spool, with a double ended clip to attach the spool to the bcd.
2nd, when deploying, unroll smb, get "slightly negative", take a large breath to become neutral again, make sure you have control of real and smb so you will be able to release quickly and easily.
3rd, remove reg from mouth, exhale (nearly) completely into smb, buoyancy does not change much as you have not taken a second breath, replace reg and purge, take a small breath, and as quickly as possible release smb, then you can return to normal breathing.
Doing this from about 10 or 11 ft gets me a smb that is 1/2 to 2/3 full at the surface of the pool, i figure if I can get it there, it shouldn't be to bad at 17-20 feet where I plan to release.
I think the key is to inflate on one breath, as then your buoyancy will not change much. That may mean inflating slightly deeper, resulting in a fuller smb at the surface on a single breath. In fact, I think the manual inflation may actually be easier from a buoyancy control perspective.