Compressing part of filesystem a second time

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http://askubuntu.com – I have a laptop running Ubuntu 11.10. I've replaced the HDD with a 120GB SSD, and to save some precious disk space I utilized one of Steve Hanov's tips for optimizing Ubuntu to run on a USB key or SD card; specifically, I implemented his third tip, and compressed /usr to a squashfs read-only volume mounted with a normal rw volume using unionfs. Now, I've installed another space-heavy program, and I'd like to repeat the procedure. However, I don't know how to... I can't inflate the squashfs volume to get to square one and do the same thing again, simply because there's not enough space on my d (HowTos)