adding bumper to motorcycle lift mounts

I recently purchased a motorhome which came with an Overbilt motorcycle lift on the back. I would like to find a rear bumper that would slide into the two square receivers where the lift is mounted. I would only use the bumper when the lift was not attached to the MH.

I am wondering if anyone here has any experience with this type of modification or knows where I might be able to find something like this. I realize that I could have one special built but I wanted to check here first before I go that route. Thanks.