[71RestoRod]

I've done it a couple of ways... there is certainly no need to trim the nuts, enlarge the holes or glue them in.

One way that works well is to find a nut that is just bigger than the head of the plastic piece... but shallow. You can grind it down if necessary. Tape it on the end of a small c-clamp. You get the idea... clamp the plastic into the aluminum while supporting it with the nut. You can also use the open end of a wrench with the c-clamp if you have three hands.