Your making me work
IT Policies / Desktop Only Items
Edit these settings:
Force Load Count (I'm using 3) basically how many times they can connect before the upgrade is forced.
Force Load Message (mine is below)
Your Blackberry has an OS Upgrade Available, Please upgrade
I am using the same share that I use for my Software Configurations but as I noted you could use a seperate share to only feature OS updates using WDM.
Now if I could get the self signed cert to be replaced so users don't have to accept it I'd be happy