I chose #2 and #3, for the following reasons:
#2 for flavor reasons - I like the idea of a dragon delivering a touch attack with it's tail or a succubus delivering an attack with a kiss. If trying to deliver a touch attack with a body part not normally used by that creature as a weapon, like a non-succubus trying to deliver an attack with a kiss, I'd probably introduce a non-proficiency penalty.
#3 for mechanical reasons, but with a caveat - Having studied a grappling-heavy martial art, I'd rule that you'd have to make a successful grapple check to discharge the spell in place of a normal "touch attack." I know how easy it is to get specific body parts trapped in a lock or hold - which makes them useless to "attack" with. A successful check would allow the caster to escape that lock and touch his opponent.
For example, let's say that a cleric casts harm, and holds the charge, intending it for the BBEG at the other end of the room. Before he can make it there, though, he has to get past BBEG's minion - a fighter. Instead of whacking the cleric with his sword, which he knows will allow him to advance past him on the next round, the fighter decides to initiate a grapple to tie the cleric up. This gets resolved as follows:
The fighter reaches out toward the cleric, provoking an AoO. The cleric doesn't want to waste the harm spell, so he swings at the fighter with his off hand, and misses. The cleric makes a mental note to train more with his off hand.
Step 1: Grab The fighter makes a melee touch attack against the cleric to start the grapple. "Yoink!" the fighter thinks as he gets hold of the cleric's robe.
Step 2: Hold Now that the fighter has "grabbed" his opponent, an opposed grapple check is made, which the fighter wins. With his other hand, he takes hold of the cleric's "harm" arm and twists it in ways that arms aren't supposed to twist, inflicitng subdual damage. The cleric's elbow now points at the ceiling, and, to aleviate the pressure on his enitre arm, he has to bend forward, putting him off balance. The cleric is now "held."
Step 3: Move In The fighter steps into the cleric's space so that he can better control him, and gets ready to slam his knee repeatedly into the cleric's head.
Step 4: Grappling The two combatants are now considered "grappled." With the fighter's two remaining attacks for the round, he does indeed throw knees at the cleric's head. The first opposed grapple roll resolves in the fighter's favor, and he smacks his hard, pointy kneecap into the cleric's noggin. The second opposed check resolves in the cleric's favor - he manages to get his other hand in between the fighter's knee and his head, and avoids taking subdual damage.
At this point, it's the cleric's turn. He decides that he's going to try to escape the grapple. He rolls forward, trying to untwist his arm, and, since he fails the opposed grapple roll, pulls the fighter down on top of him. He's still grappled, and now he's on his back with a very heavy fighter sitting on top of him. The fighter still has hold of his arm.
"Fine," the cleric thinks, "let's see how you like a harm spell." With his other attack for the round, he tries to push his "harm" hand into the fighter's midsection. He makes another opposed grapple check.
If the check resolves in the fighter's favor, he is able to successfully controll the cleric's arm. As the cleric struggles, the fighter puts more pressure on the arm, stopping the movement of the hand before it contact him.
If the check resolves in the cleric's favor, he is able to overcome the fighter's resistance and deliver the touch. The fighter gasps, realizes that he only has 1d4 hp left, and runs screaming like a little girl.
Just as you don't need to make a melee attack while grappled to inflict damage, I'd rule that you don't need to make a melee touch attack to deliver a touch spell. An opposed grapple check takes the place of both.