Power Caster at one time had a 5th wheel adapter but I don't see it listed on their website.
I did find this video with a DIY adaptor. Maybe a welding shop could fabricate one for you. https://www.youtube.com/watch?v=9dJjPry-Ko4
I had always planned to get a used forklift if I had a need to move the 5th wheel into a tight space. I've seen many of them on Craigslist for under $6000 and as low as $3000 in working condition.
I often wondered if one of the 4X4 ATVs like the Honda Fourtrax could be adapted to carry the pin weight and provide the ability to move a 5th wheel short distances on slightly un-level ground. I realize based on the specs for the ATV the 5th wheel is far too heavy but I once towed a 1 1/2 ton truck up a slight hill for over a block with my 1977 Honda Civic to get the truck out of traffic. It was quite a sight too see.