Instead of a paste, I like to do a sugar soak with lizards. Run a sink of cool water, and add a cup or two of sugar (depending on sink size) to a cup of warm water to dissolve the sugar, then add the sugar to your sink of cool water. Soak him in it for 20-30 minutes. This might help to reduce the swelling so he can retract the area back in.
If you think it might be a blockage, while you are soaking him, gently massage the stomach and vent area. Be very gentle and don't actually touch the prolapse.
Also, make sure you are keeping him as sterile as you can until you can get him into the vet. I'd replace whatever bedding you have with paper towels for right now. I would also suggest applying a small amount of Vaseline or KY to the cloaca to keep it moist and help fight debris.
Good luck and I hope this helps.