And if so how?

if you're good with a file, and patient, no problem. start by cutting lengthwise strips off, leaving peaks between them. then go back and knock the peaks off. now dress it very gently while slowly rolling it. then get some medium grit sandpaper and roll it in a closed fist. mic it out. repeat as necessary. small cuts and multiple iterations are the way to go. patience, and lots of beer...

I want to know what frame/tubing used a 27.6 seat post. I've seen 27.4 for Reynolds 753 frames but 27.6 is a new one to me. As for solving your problem, I'd suggest a machine shop. I would think it would be a fast and easy job