There is a small essay regarding Incorporeal Creatures in the 3.5 Archive from WotC.
Of course, it refers to 3.5, but some of those rules could be used in Pathfinder, too.
In particular, I refer to these:
"As noted in Part Three, some attacks ignore the incorporeal miss chance. The list includes the following:
Force: Anything with the force descriptor has no miss chance against incorporeal subjects. This includes attacks (such as magic missile) and force barriers (such as wall of force).
Positive Energy: Unfortunately, the game has no positive energy descriptor, so you have to study a spell or effect's description to find out if it involves positive energy. The cleric's ability to turn undead creatures is a positive energy effect. The various cure spells also involve positive energy; however, to deliver a cure spell you must touch a creature and your touch is not a positive energy effect. If you're corporeal, your touch attack has a 50% miss chance and if you fail that chance, your touch attack misses and you don't deliver the spell (but you're still holding the charge as noted on page 176 of the Player's Handbook). If you pass the miss chance, you make a melee touch attack against the incorporeal creature and, if you hit, you deliver the spell. The rules don't say so, but you use the same procedure for any other touch range spell. If your touch attack avoids the miss chance, a successful hit delivers the spell to an incorporeal recipient, even if the spell is not a positive energy effect.
Mass versions of cure spells, such as mass cure light wounds, that deliver positive energy over a distance, don't have a miss chance against incorporeal creatures.
Negative Energy: The notes for positive energy apply equally to negative energy.
Ghost Touch Weapons: Weapons with the ghost touch property ignore the incorporeal miss chance.
Incorporeal Attackers: Any attack or effect that an incorporeal creature launches ignores the incorporeal miss chance.
You can splash an incorporeal undead creature with holy water to damage it, but the attack has a 50% miss chance. The Player's Handbook says you must be adjacent to an incorporeal creature to use holy water against it. There's no reason, however, why you couldn't use the rules for splash weapons. Just aim the holy water at a grid intersection near the creature as noted on page 158 of the Player's Handbook. This trick works only if the incorporeal creature is adjacent to the grid intersection you choose and if it is not getting total cover from a corporeal creature or object (see Combat Tactics for Incorporeal Creatures).
An incorporeal creature's lack of a physical body makes certain special attacks moot. For example, a corporeal creature can't bull rush or overrun an incorporeal creature (but it could try to move into its space; see Using Creatures as Cover). A corporeal creature also cannot trip an incorporeal creature."
You can easily substitute the 'miss chance' of 3.5 to 'half damage' of Pathfinder, and use these rules as guidelines (until we have an official answer, that is).
In your case, Channel Energy, being Positive Energy, would deal full damage to Incorporeal Undead (and full Healing to Incorporeal living beings).