Hi,

to me it looks rather like paper towel than a prolapse. But I think it's better to wait for the experts opinion bevore pulling it. Also, the frog came quite far on its own - you could wait for some hours and see if he makes progress in getting rid of it...
A bath could support him, as suggested e.g. for impactions (http://www.frogforum.net/pacman-frog...t-pooping.html)

Apart from that he looks like a healthy frog, hope he will be fine.

good luck!