I had to cut off the foot rest mounts on my MC16 and ended up with a fairly thick piece of epoxy to remove (except where i cut too deep, but that's another story).
Sanding looked to be really hard in this place, so tried a chisel, then discovered that if i held it vertical and used it like a scraper I'd get thin shavings, worked really well.
Key was a VERY sharp chisel, a sharp scrapper blade should also work. Takes off the high spots without sanding thin the surounding area.
I should mention, this was well cured exoxy (1 yr +), not so sure how well it will work on fresh soft epoxy, but try after it's hardened well.