Bob, you can use, if you have, the Jobo Duo-clips which allow you two (2) rolls of 120 on one reel. Take a bit of getting use to but will become easy.
I've gone thru this until with every combo / dev / film around so If I can help just PM me. If you follow the Jobo instructions for your specific unit, life will be good. I've been bang on all the time execpt when it was my bad.