First, I solder all the pins together with a fine wire (single strand of a stranded wire) except the heater connections. Then I hook the heater up to the usual place on the board and ground the fine wire. this will light all segments up.
Next I take a picture for vectoring, using a high rez cam on a tripod head on. I usually take 5-10 pics at different exposures so that I can get the zinc sulfide ones without blooming since they are by far brighter than the rest.
After that, I vector it, and then desolder the wire while still leaving the heater hooked up, and finally I use a micro hook clip lead + a wire to do the pinout. connecting plate 0 (left most one) to ground, then touching the grids to see where it connects. This is repeated with each plate connection until all of them are traced out. It doesn't take a terribly long time to do even though it sounds like it.
Lots better than squinting at traces on the VFD which can sometimes not tell the whole truth. See the back side of bambino boxing. the traces go along the top, but there's connections down to the plates.