If you are prepared to go through quite some trouble, you could try to shrink the file system and logical volumes on the LVM2, which would then allow to shrink the physical partition itself.
Since this is the root file system, you need to use a Live CD (Fedora, Ubuntu, Suse etc).
Here's comprehensive advice by someone who did exactly this in order to install Windows 7 on his Fedora box:
http://dotnetdave.wordpress.com/2009/11/07/my-dual-boot-nightmare-and-a-good-procedure-to-shrink-partitionlvm2ext4/That guide is invaluable, because it deals with the actual situation, i.e. a Ext4 filesystem on the LVM.
Similar howtos exist, but they all are addressed to LVMs containing ext3 filesystems. But some may still serve you as cross references, I guess:
http://fedorasolved.org/Members/zcat/shrink-lvm-for-new-partitionhttp://forums.fedoraforum.org/showthread.php?t=154874
