Sorry, but there's no sane way to do this in general; who knows what rubbish is lying around on that filesystem that might (and does, in my experience) cause the installation to blow up? The installer has no particularly sensible way to clean out just the right bits, and even if it did I would absolutely not want to encourage people to use this without making a backup. You say that it worked in Dapper, but in fact I got a huge number of bug reports about breakage due to this type of Dapper installation.
There's already a bug asking for some more fine-grained control here, which I will consider at some point, but your best bet by far is to make a backup or split the partition. ** Changed in: ubiquity (Ubuntu) Status: Unconfirmed => Rejected -- herd2 gui installer forces format of partition https://launchpad.net/bugs/80793 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs