If you build a wiring harness using stiff wire with no excess cable lengths, you can put the electrics inside the guitar using just your fingers and some needle-nose pliers. I've done it. Some cotton around the toggle switch helps but it's not really necessary.
It's a bugger of a job Simon I have 5 here I got to do and it still frustrates me to death its the worse jobs of building a guitar id rather have a big dent in the body than tackle the pots on a hollow bady 😫