I have used a 5th string capo on all my banjos, and found them fine. I appreciate the problem of drilling into a decent instrument, but its best done with a model makers drill which will give very small pilot holes. My real problem has been taking the thing of to transfer to a new banjo, as it leaves two holes in the kneck. A bit of filler and a dab of a polish restoring crayon usually works fine. To avoid any rattle from the disengaged capo, I usually leave it on at the second or third fret and de-tune the fifth string to its normal pitch. Gives some nice unusual effects.

Keep on picking - strumming - whatever