I was thinking the Tannus as well. On their site that didn't look like they come in 27 in. If you could get a 700c wheelset the Tannus or Marathon pluses would work well.
I’ve mounted Greentyre’s solid tires - also supposedly in the 700C size - onto 630mm rims. It wasn’t noticeably more difficult than mounting them on the intended size.
I’d assume Tannus would behave similarly.