I tried something I'd read and it worked out very well for me.
I CO 1 extra stitch than the pattern called for. When I was ready to join, I slipped the stitch on the end of the right side to the left side. Knit the first 2 stitches together and you are good to go.
OTN: my first attempt at any type of mitten - doing fingerless
Oh...and I'm heajames on Ravelry