It looks like there might be enough room to move the bottle cage forward on the down tube. If so, an adapter would be easy enough to make. Get a piece of suitable material and drill 4 holes in pairs. One pair for the current mounting position, and another offset some distance for the bottle cage.
Then it's only a question of how fancy you want to get, ie; you could countersink the "frame" holes for a clan look, and use thread inserts pushed in from the back for the "bottle holes".
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