Encrypted root, use file instead of passphrase??

I have succesfully installed openSUSE 11.2, i have encrypted the root filesystem by encrypting the LVM type partitions. Now my question is, is it possible to unlock the root partition with a file instead of a passphrase?? I have already set my DATA partition to open with a file on my USB stick.

Please help, i only have a temporary simple passphrase to use until i resolve this issue.