[rhl]

My first thought would be
3/4 or 1/2 inch diameter pipe, maybe 1-2 inches long
A short eye bolt.
An eye bolt the leangth of the pipe.
One but.
2 end caps with holes, just big enough for the eye bolts to fit in.
Insert a short eye bolt and nut into one end cap.
Glue the cap onto the pipe.
Glue the second end cap on.
Insert this into a pail of water, with the eyebolt up.
Wait until the bubbles stop.
Insert long eye bolt into the end of the pipe.
Freeze pipe.

Notes
The longer and wider the pipe, the longer it will take to freeze, or thaw.
I would first test with an easy to escape. Maybe use a rope, or string, that can easily be cut.