If a wizard has High Magic spells deal these out before the game. Deal to the highest level wizards first, and then to lower levels, rolling off for those of equal potency.
In the case of High Magic spells do not deal one spell per magic level. Instead, deal one card per magic level plus one extra. Once a wizard has received his hand, the player is allowed to choose his spells from the hand he has been dealt, and the remaining spell is shuffled back in the deck. Then the next wizard receives his spells in the same way, then the next, and so on.
Because a High Mage has some choice of spells he can tailor his magic more effectively than other wizards. As High Mages are supposed to be the most powerful in the world this seems only fair. This is an important advantage, because many of the High Magic spells are only of use against specific armies. For example, the spell Banishment is only of value against Undead or Daemons, and would be of no value against a Dwarf or Bretonnian army, for example.