I would just knit the three together and then continue with the moss pattern as it fits. So, for example if the three stitches you knit together would have been a kpk, then you would just continue with pkpkpk after that. Make sense?
I would do this if the three stitches are kpk. If the three stitches are pkp, I would purl them together. Clear as mud?
Thanks all - this seems to have worked out okay. I get a 2nd go with bootee No2 now! M