I'm surprised the folks who make hides haven't come up with this one yet. I sort-of discovered it by accident while making a hide from a plastic bucket. I have a female BP who would rather wear a small hide like a hat (especially after a large meal) than move up to a larger size.
The bucket needs to be tapered rather than straight sided. I noticed that after I cut the bottom of the bucket off to make a hide out of it, the piece that was left (top part of bucket) fit perfectly over the overturned bottom (like a sleeve). Ah ha I says to myself. I cut the usual hole in the bottom part, and a slot in the sleeve part, so that as the bottom piece rises up as my chubby girl enters, the sleeve stays on the floor of the enclosure. The hide adjusts to the size of the snake all the while gently hugging her from all sides and from above.
Feel free to run out and get a patent on this. I just don't have the time.