I added 1/3 oz to my Contender's left wingtip to get lateral balance (two .36 cal lead balls drilled and pinned with "T" pins in line with the plan C.G. outside of the last rib on the tip former, then epoxied in place). I figured that a fully symmetrical low wing with no dihedral would be extremely critical of balance.

If I were in your place I would cut an access hole inside the last rib (on the bottom of the wing) and lash & epoxy a wheel weight to the rib. No point in disturbing that wing-tip covering job.