2 1/8" is the same as a 54mm. A 2 1/4" would be little bigger but probably get it tight enough. The other option would be to use a screwdriver and keep hitting the edge of the nut until it tightens. This is o.k. usually for removal, but there is know way of knowing what torque specs you have tightened it back to. Especially since you have to really tighten it to reset the hub onto the spindle. I would either give the 2 1'4" a try or wait and get some help. If it were me, I would just order the right socket. You have enough time to get it mailed to you, and then you have the right one instead of wasting your money on the wrong one.