Tested this with my 7942 Phone with CUCM 10.5.
It doesn't Work. When i Press CFwdAll and enter the Number it simply give fast busy tone and disconnects.
If it is set from the DN Web Page , Phone will display Forwarded to Message but the actual call forwarding fails with message Call Cannot be dialed....
So the only option is to disabling the CFwdAll by removing the Softkey OR by applying proper CSS restricting the Access OR Some Programming using APIs Might Help. Below might be of interest for you.
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