Hopefully these pictures are self explanatory. But if not the Brettonians have been magnetised to their movement tray. 3x1mm neodymium magnets from eBay glued to the movement tray and 2 bits of a paperclip glued discretely inside each mini's base. That's all there is to it, and no more collapsing units while manoeuvring. Cool for me at least.
Photos now back in place. The loss was due to a reorganisation of the Picassa Web album they belonged to.