Hmm... rsync is designed to keep two sets of files synchronised, so ideally you should have the same amount of space on both the source and destination. If you are just copying specific files I would use scp.
Anyway, one thing you could do is find /source/dir -type f -mtime -1 | while read f ; do rsync $f destinationhost:/destdir or something along those lines to only transfer files updated in the last 24 hours.
Annihilannic.