You've got the right idea. If you want to keep the sloped bind off, you can do short row shaping in preparation of three needle bind off.
Or you can just knit those extra rows all the way. I've done it both ways and to be honest, I don't see much difference. If it's a very fitted sweater, it might make a difference, and I don't make very fitted sweaters.
If you want to do the short row shaping, let me know and I'll try to explain it.