In my experience you can reduce weight by up to an ounce depending on the type of pin, by changing to G-10 or aluminum
Drilling the butt doesn't reduce weight by any large amount
Helium Balloons and strings should work!
Seriously you can get a long .421 drill bit and have at it and then tap it with a 1/2 13 should you want to go back ever.
Drilling out that deep into the cue is not my bag but it is an option. Of coarse anything you do front or back will change your balance point.
You can drill it a little at a time and judge the feel of your new cue incrementally. How do you really know 1 oz is what you want.
Rick