I'm posting photos to follow up.
I clamped the stock in the vise and used wood scraps to bend the forend, going a little past straight:
I heated it with a heat gun on a low setting, moving constantly to avoid scorching. I got the wood very hot to the touch. I'm not sure how long I was heating it - at least five minutes, but less than ten I'd guess.
After it cooled, I removed the blocks. As you can see, it's improved, but not perfect yet.
Here's the "before" shot again, for comparison.