I need to run VACUUM FULL with no available disk space

I have one table that is taking up close to 90% of hd space on our server. I have decided to drop a few columns to free up space. But I need to return the space to the OS. The problem, though, is that I'm not sure what will happen if I run VACUUM FULL and there is not enough free space to make a copy of the table. I understand that VACUUM FULL should not be used but I figured it was the best option in this scenario. Any ideas would be appreciated. I'm using PostgreSQL 9.0.6