Basically you want https://www.youtube.com/watch?v=-G19h1poSoA this with Office365...
I don't think that will be doable without allowing all of Outlook.com but we'll try...
Are you blocking Web Mail with a Web Filter?
Make sure the Multiple Security Profiles feature is enabled for that one.
Go to Security Profiles > Application Control and select Create New in the top right corner
Name it "O365"
Select the action for all categories to Block
In Application Overrides select Add Signatures and search for these three:
Select them and hit User Selected Signatures
Set action to Allow
Create a new policy without your Web Filter profile and use this Application Filter
Move it on top of your other policy