If there is a little bit of space between the spar and rib you could try sliding a piece of .016 (or thicker) sheet metal between them. This would protect your spar from getting damaged by any tools you use. Ideally you would want to curl the piece to get the right radius and then slide it on the spar without making any scratches.
Instead of aluminum you might be able to use a piece of an old plastic bottle. This this would already have the curl in it.
Whatever material you use don't let your tools penetrate though it and touch the spar.