Have you considered using BTZS tubes? You could use your Jobo for developing most of your film and the tubes for the individual sheets that require different development times. You might also consider a "slosher tray". The tray avoids scratches and provides very even development and allows individual sheet development.
I use a Jobo for just about all my film development. I have tried hangers and trays but the results are not as consistent as with the Jobo. For 4x5, I will use the slosher as needed. The only downside to the slosher is you use more chemicals than with the Jobo or BTZS--and you have to do it in the dark.