I suppose it could be done but it wouldn't be cheap. I'm thinking it would have to be custom made, and you'd have to fabricate the mounts that attach it to the bed wall.
I will say this, it's not likely that those cords would come off. We had a pop-up that had a setup like that for 10 years and never had an issue.
A friend of mine rented a pop-up when his kids were little (he has 8 kids!) and not having experience with setup he forgot to attach the bungee cords to the bottom of the bed. One of his daughters fell out of the bunk that night, I think she was 3 or 4 at the time. She wasn't hurt, just startled.
But that's the point, so long as you double check that the cords are in place you will not have a problem.
Just go camping, don't worry about it, and have fun!
Chuck D.
โAdventure is just bad planning.โ - Roald Amundsen
2013 Jayco X20E Hybrid
2016 Chevy Silverado Crew Cab Z71 LTZ2
2008 GMC Sierra SLE1 Crew Cab Z71 (traded)