You might try OneSwarm from the University of Washington. See the wiki article at http://en.wikipedia.org/wiki/OneSwarm which, as I understand it, is a a bittorrent P@P system but which allows you to specify who may participate in the share. From what I have read you should be able to set up a share between two remote computers and have the file(s) transferred like and other bittorrent transfer.
Another possibility might be DropBox from http://www.dropbox.com/
The free version allows files up to 2 gig. This would likely be easier to set up than OneSwarm.