Might not be what you have in mind, but this was what I kind of imagined how someone could depict Ben surviving.
The idea being that Ben went into exile on Tatooine or something and Rey came to find him. I think it makes more sense than Rey going there to bury the sabers. This would also force you to remove the old woman and “Rey Skywalker” bits, but it seems like you already have that in mind.
The only “issue” is Ben still wearing his Kylo garb. But, theoretically, a person could film themselves wearing Tatooine style robes and a poncho, which would mostly be seen in silhouette only so detail isn’t important.
If you wanted that CU shot of Ben, it would require you to mask his head on a new body with a new outfit. But that shot isn’t totally necessary either. Might not be what you want at all though.