Boot from SD card is not supported. Also, for a given image, the partitions on the internal flash are set at flash time, and are very tricky to change afterwards.
My recommendation would be to create a large linux partition(s) on an SD card, copy everything in /usr to that portion, then change your fstab to mount that external partition as /usr at boot. This means that the SD card has to always stay inserted, though. Would that be such a big issue?
Thank you David!
I'll try that!
It actually worked very well. So thanks again David!
I might return to the issue of whether it is possible to change the flashall script to set the partitions up differently when installing ubilinux at some time in the future.
Right now I'm off to see why teamviewer wont work :-(