The aerobic step next to the bench might work! I'm going to try it tomorrow when I do step ups again!
So many great ideas here, so if the above doesn't work, I might be able to try out some of them. Unfortunately, I don't have a gym ledge, a pickup truck (though I'd like one), concrete garden benches or planters (though hopefully this will change in the far future as I get this yard cleaned up), and I live in a single-story house with no stairs.
The lumber idea would definitely work so long as it didn't get halfway completed and then sit around for a few years in an unfinished state like certain other projects I've attempted, heh. I'll just have to pray that the aerobic step next to the weight bench works!
Thanks for all of these great ideas!