In the following assembly, how can I trap the bar withing the holes?

1. The bar is free to move in any direction. Up - down - left - right, anywhere.
2. But when I insert it into one of the holes or both of them, it should be limited to move only within the hole(s). In other word the bar would be prison within the holes. While the bar is within the hole(s), it can move up and down, but its left/right/diagonally movement should be limited within the holes. When the surface of the bar touches the surface of the hole, its movement in that direction would be stopped.

I've seen this solution, but I couldn't imagine how to change it to fit my need.

https://www.engineersrule.com/impossible-modeling-challenges-part-5-volume-limit-mate-keep-prisoner-jail/ 

A sample assembly is attached.

Any kind of help is much appreciated.