Hey Jigeye. How about either of these. The first one is from Great Planes GPMQ3360 4-40 Threaded Inserts 4 pcs. Or maybe these from Du-Bro http://shop.dubro.com/p/e-z-mount-co...-size-aircraft They have two sizes.

Another option is to build your own mounts, from some light ply, and put the blind nuts on the correct side. Just another thought.