The basic idea is that you cut a jig to be used inside another jig. A nice rectangular reusable jig with cutouts for your bands. Then when you want to use it, you cut a jig to slot the rectangular jig into. Everything else proceeds ad normal more or less.
I use corner jigging instead of cutting the whole thing out, you only need to lock it in the correct spot, and it saves a lot of time and materials to just cut the corners out of cardboard and slot the jig into place.
Writing all this out with pictures is really inadequate; doing a full write up with pictures and whatnot would be really good but also take forever. Sorry, no time to get to that.