SRAM Red eTap on Ultegra bike

Cost aside, a carbon framebuilder or repairer could likely figure out a good way of doing it.

If tire clearance considerations allow, a simple way would be removing the existing hanger and building up the needed area to 31.8 or 34.9, then doing a hanger adapter. (If by some chance it's both a round tube and a standard diameter, you might not even need to build it up, but one or both of those probably isn't the case.) This would be a fabrication-minimal way. Or they might just bond on a new hanger. Or they might feel comfortable just relocating the holes for the existing hanger.

I would look askance at filing it unless it was clear that a good amount of material would remain. Weakening that spot too much could make terrible things happen. That said, if you tried it and it didn't work, you will almost certainly have outs, either from a third party or from Cannondale. I've known them to replace SuperX FD hangers as a paid repair and I assume they're able to do this frame as well.