I think technically two-weapon fighting only applies to touch attacks if you are using them as a secondary attack, e.g. making a regular attack with a weapon, then secondary attack with the touch. The reason I think this is that natural weapons don't use iterative attacks; if a monster has a single slam attack, for example, it can only make one slam attack no matter what its BAB is. A shadow gets one touch attack no matter how many levels or hit dice it has. From the SRD: "the number of attacks a creature can make with its natural weapons depends on the type of the attack—generally, a creature can make one bite attack, one attack per claw or tentacle, one gore attack, one sting attack, or one slam attack (although Large creatures with arms or arm-like limbs can make a slam attack with each arm). Refer to the individual monster descriptions."
However this sucks, so I'd consider a houserule it so you could make iterative and off-hand attacks.