This is a customizer for generating blanks to fill in unpopulated switch holes in most types of car and truck dashboards. It's kinda messy and not really cleaned up yet but it should work. Just take measurements of the hole you want to fill, plug in the numbers, select how many retaining clips you want and where, and presto! With any luck it will fit perfectly and look stock.

Recommend printing it on its side such that the most important retaining clips are on the sides and the less important ones on the top and bottom... this will give you the most strength for the retaining clips when printing. You will need to use supports to print it this way, however, while the default orientation does not require supports (but the clips will be weaker)