You can buy a tap and drill set at the hardware store for a few dollars. This includes the tap & the correct size drill bit.
8/32, 8/24, 10/32, 10/24 would be common SAE sizes, or metric sizes a bit less common at the store.

Sheldon's info is all you need. Vice-grips can also be used for makeshift tap handle.

Tapping aluminum is pretty easy, and putting a small hole in your stem is not likely to shorten your life or ruin your smile IMO.

I would make the hole on the side of the horizontal part of the stem.