I think I might have this resolved. With your input I think I figured out how to get this to work with some modifications.
First, our standard users are not able to run the IU without Admin privileges. Second I was following the steps in the document that was provided in the link above (http://www.symantec.com/docs/TECH104363) however, in Step #6 of this document the path that is referenced does not exist on my clients.
Then I got to reading about the Third Party Deployment so I went into my SEPM and changed the policy to also allow for that and then generated a new install package with this feature enabled, thinking that once I installed this that I would see the "inbox" folder in the path C:\Program Data\Symantec\Symantec Endpoint Protection. Well I didn't, however, under C:\ProgramData\Symantec\Symantec Endpoint Protection\ there is a folder entitled 12.1.671.4971.105if. There is an inbox folder under this location. So I was logged on as a standard user to see if I could manually update the definitions with the .jdb file and when I tried I got access denied. So I logged back on as the Administrator and changed the permissions of that folder to be full control for Everyone. Then logged back in as the standard user and dropped the .jdb file in that folder,
Almost immediately after dropping that file in there, another folder appeared with what looked like the name of the .jdb file followed by a series of numbers, and then almost immediately after it appeared, that folder as well as the .jdb file I dropped in there disappeared.
When I checked the dates on the definitions, they were updated to 5 Jan 12 (previously 4 Jan 12). So I want to do some more testing on this, but I think it is working.
One note: The client is primarily going to be stand alone, not connected to a network and unmanaged by a SEPM. But in order to get this to work, I had to add the client to the network so that it would check in with the SEPM after I installed the package. The shield icon in the system tray appeared with the green dot indicating that it was updated by the SEPM. But I don't think this will have any affect on updating the client from here on out when it is off the network because I am able to drop the .jdb file to it.
So the instructions in the above referenced link worked, but the location of the inbox was not shown at the path listed in the document. I plan to do a little more testing tomorrow and will update this post to hopefully resolve this issue.
Thanks