On recent tip top installation, I used some "Cheapo" rod tip glue, the stick you heat w/ a lighter type that came w/ a 3 pack of various tip sizes...well, after I put on the tip, added a decorative trim and flexcoat finish, the rod tip glue failed and began to spin....on that note, I'd say the 5-min epoxy mentioned above is the way to go (I wound up redoing mine that way...)
A trick i've seen (but haven't tried) for shimming an oversized tip top is to use threads either traditionally wrapped, or run lengthwise down the blank to take out the "play". In other words, on sizing, a top slightly bigger is better than one that won't fit. I don't think I would sand a blank top to accomodate an undersized tip top, as this would weaken a critical spot......