Dispel Scroll and Cube of Darkness should get you 2 turns of defense.
He's unlikely to be in range turn 1, unless he goes balls out throwing his level 4 wizard at you.
So now you have ~3 turns to figure out how to kill a T3 model with 3 wounds and at best a 4+ ward.
The solution comes down to, kill the wizard. Dead wizards can't cast purple sun.
You want a dirty wizard killing trick?
Take 2 scar vets. Mount both on cold ones. Give one the stubborn crown.
Have the one with the stubborn crown join the other, making a unit. Deploy them 1 wide.
Charge into the wizard bunker, touch the wizard.
Scar Vet in front issues a challenge. If he accepts, the guy in back is making supporting attacks on the wizard, and the unit is stubborn. If the guy in front is killed by the ASF (or init 5 great weapon) attacks, then the stubborn guy in back steps up and makes full attacks on the wizard (and is still stubborn).
If he doesn't accept the challenge, all the ASF attacks can only hit the character in the front, as they aren't touching the rear scar vet during their initiative step. Now you're making attacks and supporting attacks (or just the attacks from the rear guy if the front dies).
I used to do this with a goblin big boss and a goblin warboss, both on wolves, scar vets are more expensive, but it should still work. Another option might be a chief cube. 4 Chiefs with extra hand weapons is 42 points each. They could join up 2x2 and do the same type of thing. Init 6 would mean you swing before the great weapon elves.
The whole key is that you're basically sacrificing the front hero so the back hero can swing.
-Matt