Here's a malt chart that you might take a look at to get an idea of the potential for popular grains. I wouldn't think steeping would give you very high efficiency, but:
If you add say a pound of crystal 20 (1.035) at say 60% efficiency, that would give you
35 * .6 = 21
add that to 5 gal batch and get
21/5 = 4.2
So maybe you'd be adding around 1.0042 to your OG. That may be a bogus method if the steeping grains can't convert by themselves.
It's probably a minimal increase, but you could also check your gravity after steeping and calculate how much less extract you need accordingly. I probably wouldn't bother and would just take note of the difference after doing a batch.
