Kwired,
What parallel conductor rule are you refering to? Which code section requires that you have to tap all parallel conductors?
310.4 is a place to start that has most of what applies.
The purpose of using conductors in parallel is to make multiple coductors effectively one conductor. If not joined at both ends this does never happen. If you make a tap in the middle of the effectively larger conductor but only connect the tap to half , or third, or fourth, etc of the effectively larger conductor you have disrupted the whole purpose of calling this one conductor as you throw off the load balance on the set. If you tie all conductors of the parallel together where making a tap then you are taping the whole conductor and not just part of it.
Take our two 500's in parallel in this thread.
500 has an ampacity of 380 @ 75 deg C.
Parallel two of them you effectively have a 760 amp conductor.
Make a tap off of one of them you are not taping a 760 amp conductor you are taping a 380 amp conductor.
This also creates another problem because that single 500 is not protected at its ampacity it is protected at the parallel conductor ampacity making it a tap conductor itself. You can not tap a tap either.