It's interesting to see how many people are doing this, as the few times I tried using an old graphic EQ for a boost, it was very noisy compared to an OD as boost. Conceptually, it's fine, I just never had any luck. Now that I think about it, I probably haven't tried it since the 80's so newer EQ's are probably better in that regard.
I played around with a parametric EQ with more luck, but never bought/owned one so it was just a one off at someone's practice space.