I had a Bontrager carbon post come to bits on me. One of the really early ones – I think it was made in conjunction with Titec.
Anyhow. Cleaned it up, and remembering a tip from a lecturer at uni, stuck it back together with the slow-setting araldite.
Left it leaning on a radiator for about a week to cure nicely.
Good to go. Worked for 8yrs until I sold it.
Drilling/riveting would be pretty pointless as if it’s moved enough to need that for integrity, it’ll be in bits in no time.
Rivets are usually only used in this sort of assembly to hold it still whilst the glue is drying, and as it’s a part that doesn’t matter if rotationally it’s off cock, then I’d not fret.
YMMV