SG,
Yes, you can place foam or rigid fiberglass in front of the wood panels, but you must space it away so it doesn't touch the panels at all.
I'll also mention that unless your room is very small, you should build the "system" of three trap types as explained in the article. That will give you the correct amount and balance of absorption. If you feel it's still too live after they're all installed, then you can consider covering some of the wood panel traps.
--Ethan
