I was thinking a wheel and tyre from one of those big snow wheel bikes or something. Almost wanting to make a circus monstrosity. I am seeing potential for near recumbent seating.How big of a wheel are you thinking? I have had in my head a build using one of those box store Genesis 32" wheels in the back or a 36" if I could find one cheap with the wheel coming up high enough to almost be a back rest. It would be a proper posture reinforcer. Anyway, I was just going to do bolt on drop out additions. I don't know if it would work, but it would try to make it one piece so that it bowed up around the top of the tire in a U shape with the ends reaching around to form the drop out extensions. I didn't figure out how I'd connect to the seat tube and/or seat stays. If I could weld, it would be easy.
If this frame were in better knick as far as originality is concerned as well as the availability of the pin that the beam flexes, it would be a different story. Hence the desire to do something with this.