Hi! I've done numerous pieces, particularly afghans, that I blocked, even though they were acrylic.
I put them in the washer on gentle with a soft soap (like Ivory Snow) and then lay out the piece on my blocking table. I use a lot of blocking wires to make sure I can even up the sides and then just let the piece dry.
It comes out really nicely, much better than if I'd just left it alone or washed and dried it in the machine.
I wouldn't not block a piece of acrylic knit. They really do look so much better.
Then, too, the stitches are set and future washings and dryings don't necessarily need blocking!