Editing with proxies separately from the original files

I have about 6TB of files for project that was shot in 6K. 

What I would like to do is create very low quality proxies and edit SEPERATELY from my desk hard drive.

So save the proxies ideally on a 512GB flash drive and when the project is done, re-link to the original files for export. 

Is this possible or do the proxies HAVE to live next to the original files? I'm assuming this will cause an obvious glitch with the toggle proxies option if theres nothing to toggle to.