Well after all this scheming and dreaming (YES, last night as I was trying to :zzz: ), I realized that there was NO WAY I would be able to pick up stitches around such a long skinny rectangle and work in the round. It was just physically impossible.
So I'm back to doing this as per the pattern (ie. not in the round :( ) but I think I will still try my hand at a bit of intarsia by adding a skinny stripe down the middles of the side panels. Of course it will be done flat, which may be better to practise that way anyhow.
Thanks again Ingrid, I'm sure I'll use the other method someday too, just not on this project unfortunately.