Brummel on a closed Shackle/Ring

[GlennB]

I am trying to spice 5/16" endura on to a closed ring (from a toggle) to replace a running backstay. I have the book, read and spliced a mcdonald brummel with success, but there does not seem to be a way to spice it on to a closed ring.

I have seen references to being able to do this with a Mobius Brummel, but can't figure out how that would work either. I do have access to the other end (about 50' long).

Ideas?

Glenn