You are doing exactly the right thing. I too had an oversupply issue with my 2nd child and it is painful.
Pump off a little bit of milk from both sides so that you are not as hard as a rock (I froze this for later). I suggest that you do it right before nursing. Otherwise, your baby will get a lot of foremilk, and not as much of the rich hindmilk.
Don't pump too much. You are right that you don't want to empty, because that will signal to your body to make even more.
I went to nursing on 1 side per feeding to get my supply down to something manageable (nurse, take baby off to burp, then put back on the same side instead of switching). I would nurse on 1 side and then pump about 2 oz from the other side (pump just enough to relieve the pain, not to empty).
Some more good tips on kellymom - http://kellymom.com/bf/got-milk/supply-worries/fast-letdown/