Tag - I'd definitely test the Dremel idea first if you go with a. grinding cone - they will often clog almost immediately (unless you go really slow and maybe use a lubricant - water may even work) - and are very difficult to clear afterwards.
A countersink followed by some waterpaper and elbow grease will be the best way in my opinion.
I'd recommend a countersink, but I'd tell you to get it from Amazon rather than Harbor Freight for two reasons. First is because the countersink identical to MakoPat's I bought there was UNBELIEVABLY dull and poorly ground. Usually harbor freight was passable, but this would only countersink butter if it were warmed up first. Frozen butter? No fucking way. The other reason is chatter. Countersinks have a real problem with chatter, particularly if chucked in a power drill. Even on rigid machine tools they can be a pain in the ass though. For that reason I'd recommend buying one with the minimum number of flutes possible, a single flute or zero flute countersink. Just my 2c.
The Dremel stone once use on aluminium will clog and presents a danger if ever used on steel afterwards.
Sometimes this can cause a sort of explosion. I will look for a link. The countersing is a harder metal than aluminium, is inexpensive, and will last for years without clogging.