Nothing, sadly
That's the major setback of being an offensive mage - you are pretty much forced to wait on the game field to pass the time and regain mana.
Alternatively, if the battle allows it, you can try the cheesy way of gaining mana - a few stacks of summoned thorns, poison cloud lvl 1 from glot over them and magic spring. Sadly, that doesn't always work... So if you can, use chargers when the battle allows it to regain at least some mana, that should also reduce the wating time.