It seems there have been several (not wholly satisfactory) attempts to make a film version of The Invention of Morel and Last Year at Marienbad was inspired by Bioy's tale. (I shall have to watch that one.)
The fugitive's obsession with Faustine reminded me of Nicholas and 'Lily' in The Magus by John Fowles. It's very hard to translate these gripping stories of illusion and obsession to the silver screen because they depend so much on the representation of inner states.
I suppose that if you wanted to write a successful script based on The Invention of Morel you'd need to fluff up the mystery surrounding what passes between Morel's friends on the island, extending some of the characters that he only gives us a glimpse of. A bit more intrigue essentially.
There's possibly also scope for writing a kind of spin-off story about a being that appears to be an ordinary person interacting with friends and colleagues, but is in fact an outsider looking in that has previously studied each scene he participates in a great many times and has decided to try to insert himself and act as if he belongs there. You could build quite an interesting movie plot around that little conceit alone. (And perhaps this individual would not be as forever cut-off as Bioy's narrator and could suddenly announce that he had been fudging his life all along!)