If you are just wanting to move the data from one drive to another, you could try something like Clonezilla (http://clonezilla.org/) to make a bit-by-bit copy of the existing drive to the new drive. Basically, you will plug the new drive into the existing system, boot using the Clonezilla disk, and clone the old drive to the new drive.
Since it will not recognize the encryption on the first disk, it should do a bit-by-bit copy of the drive, which should then act normally when you boot, retaining the encryption. It has been a while since I tried it, but I was able to use it on older versions successfully, and I recently had a customer do it successfully as well.
Otherwise, you could just do a normal backup of the data and migrate the data to the new drive, then install SED and encrypt the drive.