Thats very, very easy. I'm still working but in 2 Hours I could make you one.
If you cant wait, follow my steps.
1. Create a new Aura with "Icon".
2. Go to "Triggers".
3. Select Trigger Type: 'Status'.
4. Choose "Cooldown (Spell)".
5. Insert the Spell ID or Name (Pillar of Frost).
6. Go to the "Load" Page.
7. Select 'Show only in Combat'.