How to turn a pull up into a diaper?

I have with me 2 pull ups and bananas and some suppositorys and I wanted to do the banana dare but I’m not sure the pull ups will hold the mess, so my question is how can I secure these until I can buy normal diapers

I would not recommend trying this in pull-ups unless you can protect your furnishings or floorings from the mess. Pull-ups are usually very loose and won't hold up to that kind of punishment without falling down or leaking everywhere. I have a sheet of vinyl I put on my recliner and cover it with a towel in case I overflow.