Is there an easy way to un-root Android 2.2 on Droid X rooted via z4root?

Is there an easy way to un-root Android 2.2 on Droid X rooted via z4root? The reason is that I would like to apply a Gingerbread 2.3 update from Verizon, and that update ALWAYS fails to install. Since I never had a custom ROM on the phone, my first guess is that the problem may be due to being rooted, but I don't see an "Unroot" option in z4root. Please note that factory reset is NOT an answer I'm looking for.