Ive been here...
I recently did it with one of my custom painted shells, which i nearly cried, luckily it was only the rears, so i swapped the body posts around and drilled correctly this time, covered the others with stickers.
The best bet is to use an extra peice of lexan as youve said (usually from the wheelarch cutouts), just use some muchmore double sided , and narrow in the hole with it until your happy enough.
Steven
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