Filling Unwanted Holes?

Sure.

Evergreen Scale Models styrene plastic rod.  Their #218 is 0.020" in dia., comes in a 10-pack, available at most well-stocked LHS's.  You might bore out each hole carefully with a #76 (0.020") or #75 (0.021") drill in a pin vise before inserting pieces of rod.  If you can insert them from behind until flush, then add a drop of plastic weld liquid to the BACKSIDE, that's ideal.  If you have to work from the front, do so carefully, esp. with the welding liquid.  Suggest Tenax 7r, Ambroid Proweld, Plastruct Plastic Weld as choices for welding liquid.  Testors would only be a good choice if you knew that the car body was also molded in styrene...not very likely at all.

Pre-drilling the holes has the added advantage of cleaning out any factory paint from within the existing bore which would inhibit a good bond between the rod and body.

Re painting...if you use the smallest rod, you might be able to apply a simple dot of matching paint to the outside ends. 

Evergreen makes some larger styrene rod choices up to 3/64".  You could select something larger, use a correspondingly larger drill bit.  That might make the rod plugs easier to handle but the amount of touch-up painting greater.

Just a suggestion.  Hope it helps.  It's how I'd approach the 'problem' as you've described it.   Except an Optivisor and glass of Merlot with soft classical music in the background helps me with jobs such as this!

FWIW, always...

KD

Thanks KD, great suggestion!  I have the Optivisor but no Merlot, I'll have to see what's in the liquor locker!  I think I even have some round styrene, but it may be too big, nothing a trip to the LHS can't fix.

I'll be painting the whole car once I get to a good place.  I don't think any ladders or grabs are under any decals I need to add so I think it's safe to paint with all the hardware on and then decal.

I found some .020" square styrene in my scrap box and decided to give it a try.  I found I had to dip the end of the strip in water to make it go into the round hole, but it was surprisingly not hard to do.  After I hit each spot with some MEK solvent and let it dry I trimmed away whatever stuck out of the holes.

Thanks again KD for the suggestion!