When drilling the holes for the skin to spar connection I noted 3 holes that had interference from previous rivets in the spar. I should have noted this when making the initial holes and altered the pitch distance a little. Anyway the fix is easy enough. First I drilled 4 new holes between the 3 offenders and put new rivets in those locations. Then I modified 3 # 20 rivets and made them shorter, this involves carefully using a dremel to remove part of the rivet while keeping the stem intact, then when you have that part done, just tap the stem into the remaining part of the rivet and you're done. The structural load was taken up by the new rivets so all I'm really trying to do with the shorties is cosmetically fill the hole. Worked perfectly.