Do OTA updates expire?
Here is how I solved the problem. It turns out that the BlurUpdater files are specific to the version you are running, and I didn't have the correct version.  It was a bit of work to locate the correct version.

First, I downloaded the SBF file for 4.5.608.  I then used the sbf_flash utility using the -x option to extract the images in the SBF.  I then used the file -sL XX.img command to determine that the larger images were ext3 formatted filesystems.  Then I used mount -t ext3 -o loop XX.img tmp/ to mount each filesystem until I found the one containing the BlurUpdater_VZW.apk and BlurUpdater_VZW.odex file.  Then I installed both of these files in /system/app (as root).  After restarting my device and running the check for updates I was informed that an update was available, which I was then able to start installing.