Yes I used wire insulation too, but I bought the narrowest heat shrink tubing I could find which was still much wider than the wire insulation in it's raw state, but when you apply a little heat you get a perfect tight wrap around the leads (with the size I bought which totally escapes me at the moment).
My instincts tell me not to apply unnecessary heat if you can avoid it to anything germanium, but there's nothing wrong with giving the leads a bit of a blast, they soon cool down and all the measurements go back to normal.