Use a non-sheddy waste yarn (cotton is good) in a contrasting color if you can (you aren't likely to "lose" it, but it's nice to see it quickly). Basically, you are going to have this waste yarn just hanging there, not fully attached to the glove, simply to hold the place where the thumb will be. I really thought it was a cool idea when I knit these!
Yes, you will have stitches both above and below the waste yarn. I had 2 needles ready, and as I slowly pulled out the wast yarn, I put the stitches on the needles as I came to them. I wish I had taken a pic, because like I said, I found this a very nifty way to hold the thumb.
As for removing the waste, don't use too long of a piece, and you need to leave it "free" on both ends - so no slip knots, no knitting the tails in. Just leave a tail, start knitting, and leave the end tail too. When you're ready, you just pull one of those tail ends, and it will slip out of the stitches.
Knitting homeschooling mom to 3 kidlets
Bayerische Socks by Eunny Jang in Knit Picks Risata (for ME!)
in queue: Swirl glittens; lacy raglan for me; new cabled sweater for dh