iCloud Working workaround
Using a capable Mac with Lion or Mountain Lion, create a new user account with full admin privileges, and iCloud enabled.
Use Migration Assistant to transfer the account over to your Mac Pro.
Once prompted of what you want to transfer, just select this new account. You do not need Applications, computers setting, or anything else. Just the user account.
After the transfer is complete, you should be able to use iCloud on the Mac Pro. You can remove the dummy account you just created from both computers.
Using a capable Mac with Lion or Mountain Lion, create a new user account with full admin privileges, and iCloud enabled.
Use Migration Assistant to transfer the account over to your Mac Pro.
Once prompted of what you want to transfer, just select this new account. You do not need Applications, computers setting, or anything else. Just the user account.
After the transfer is complete, you should be able to use iCloud on the Mac Pro. You can remove the dummy account you just created from both computers.