FWIW, I moved /usr/local to /home/local and created a symbolic link to it. On the Arduino breakout board I added an SD card which is mounted on /media/sdcard.
I've been downloading source packages to the SD card, building them from source, then installing them into the normal /usr/local folder.
So far I've managed to install a lot of extra packages from source without running out of room (still have 22M left on /).