Like many other miniature wargamers, priming follows the same procedure. Find a relatively large box, put miniatures in box. Spray paint from 1 direction, wait, turn miniatures around, spray paint, wait, turn etc etc.
Last night I recalled a tip from a white dwarf from ages ago. They were using a ‘primer stick’. Basically a stick with a layer of ductape around it with the sticky side out. While I didn’t have a stick, nor did I have ductape around, the second best things worked amazingly well. I used a ridiculously cheap Ikea children’s plate with a nice extrusion (the head) you can use as a handle and stuck some minis to it with blu-tac (or Pritt Posterbuddies for the Dutch). This allows you to do a full 360 spray without getting dirty hands and waiting.