I have a somewhat different bike (steel frame, triple crank) that presented me with a similar situation. Due to the low bottom bracket, the FD cage comes very close to the chainstay when on the smallest ring. There's enough space for a credit card to fit...and just a smidge more. If it's true that a credit card measures 0.7mm (based on another member's statement), then I might have 1.0 - 1.25mm clearance. That's just a reasonable guess, though. The cage has never marked the frame, and I have no reason to believe it has touched it.
Looking at your pictures, it appears that (a) you have wiggle room to raise the dérailleur a tad, and (b) the edge of the cage just overlaps the edge of the chainstay. Given that the rings only have a 12t difference, am I wrong in thinking that shifting will not be noticeably affected if you raise the dérailleur 1 - 2mm? And if this still failed to provide adequate clearance, perhaps a spacer under the drive side bb cup would help, though then chainline may not be as precise.
The first thing I'd want to do is be certain the cage is angled properly. This requires the chain on the bike, in addition to the rest of the drivetrain.
I suspect that the area near the bb is stiff enough that it would be rideable with the minimal clearance you state, but the cautious side of me would still want to bump the FD up as long as shifting remained good. Then again, if the owner would really rather be happier with a 50/34, then none of this is to bother with.