1) you need to carry a shield on you weather you use it or not.
2) the shield takes one of your hotkeys.
Okay so this is what i do i just put a spell on one of my hotkeys (one that i would want to change to without using the favorites menu) then on the other hotkey i place the shield (see where this is going). all you have to do if you want to block is either switch to the shield, or if you don't use shield's like me, you can simply hit the button a second time (before the shield is up) and it switches your spell hand to empty hand so you can proceed to block. like i said it isn't perfect but it works. if your on pc then it wouldn't be so bad seems how you'll have more hotkeys then those of us on consoles.
just figured i share this with you guy's.