How to recreate Lion Recovery HD partition?
I installed a larger drive in my MBP and cloned my original disk to the new drive using SuperDuper!  This process doesn't create the restore partition. Reinstalling Lion onto the new drive created the necessary partition for me. 

I reinstalled this using the "USB Key" installer run from a partition on an  external drive. My User accounts, applications, etc. survived the reinstall but I did have to run the updaters for the OS and reinstall Java after the Lion reinstall.

Note that I did all of this before enabling Filevault on the new drive. Not sure that mattered, but it seemed prudent.