I really don't know python but looking into to it this morning I don't think its possible. In os.path there isn't anything I can see that would have access to the remote server path, just the current temp folder path. I think this is possible but only from Apple's Cocco Framework file handler.
Objective-C has something like this
externalPath = [appleEventDescriptor paramDescriptorForKeyword:keyFileCustomPath] stringValue];
What I think is happening is that code is telling the OS to pretend the file is at the "CustomPath" instead of its real path. The result is when you open a remote file you can in the text editor display the files remote path.
Since ST2 is written in C++ I suspect it will never support native remote file path display. That is probably going to be a deal breaker for me. I really want to use this app but this one feature is a requirement for me workflow.