Oh, Jan. No other replies. Perhaps if I do the thumb gusset by doing rows 3-6 until I have increased by 12 st that would still be an odd # and not mess up the spiral rib pattern. Does that sound about right?
I liked Jan's suggestion of the plain gusset because it seemed like the cleanest solution. But, if you can continue the ribbed pattern on the gusset, I don't see why you can't continue a broken rib. It did seem to me in reading the pattern that one row of the gusset has the rib and one row, the increase row, is plain knit (the main glove continues in rib throughout). See if it seems that way to you.