I haven't tried this yet, so I'm not certain that this will work, but it was something I thought up awhile back, but never had the chance to try. Do you have any standard Weber charcoal baskets?
Do you see how the curved sides of the basket "tab into" the flat backside? If you pop that tab out of the slot and cut a new slot inward one vent hole, it should make the basket shorter and more round to fit in an SJ. Of course you'll have to trim off what is now the excess length of the flat backside and bottom of the basket.
Clear as mud?