Help with BO then CO in circular with flat pieces

[dofnup]

OK my topic title was prolly quite confusing so I'll explain:

I'm knitting a shrug (basically two sleeves joined by a flap that goes around the back) in the round cuz I still haven't mastered seaming invisibly LOL

Anywho, I'm done with sleeve number one and I've reached the point where I have to *gasp* bind off some stitches and coninue knitting back and forth to make the flat backpiece. I'm okay with that, pretty confident I can do it.

HOWEVER ...

When I'm done with the flat piece, I have NO idea how I'm going to cast on those bound off stitches to make sleeve 2 match sleeve 1. Will I be able to use the long-tail method? Or must I use single cast on or cable cast on?

Any advice would be greatly appreciated!! :D