I did the holes shielding method once on a Jazz Bass, took ages, but it's working as good as a wire soldered.
Furthermore, the grounding plate of the pickups will be "earthed" too, so it's more than enough.
You should invest in a cheap multimeter, after all, all you need is being able to check continuity, pickups impedance, pots, a few tensions here and there and maybe check a capacitor or diode. It's only a few quids well spent.