The Casting Times rules on p 613 state that the amount of Mana you can Channel in a melee round is equal to your Channel skill ranks. The rules also state that how much of that allotment you decide to Channel per CF Action Count is up to you. Question:

My munchkin player wants to cast a spell that requires Mana equal to twice his Channeling skill.

He wants to begin Channeling for the spell on his last CF Action Count of the first Melee Round and Channel his entire Channel skill ranks of Mana on that last CF Action Count of that Melee Round. He wants to finsih casting the spell on his first CF Action Count of the second Melee Round. What should I tell him?