This is exactly what I do. I'd recommend putting a couple of towels or something else in the dryer with them. It only takes a few minutes in the dryer, and I'd stay close by, as mine got jammed in the tumbling mechanism which stopped the dryer, and I had to pull them out immediately (they were fine). This is why I think some towels or something else in with them would help.
The dryer can be used to stretch them in this way, or if you want to shrink them, just let them sit and cool without putting them on your feet, and they'll shrink a bit.
I've had some that were too tight across the top of my foot, and used the dryer to stretch them out, and now they're fine. Remember that the crocs shouldn't be touching anywhere except the bottom of your foot!