Programming an ATmega328P by holding it on an Uno's
It's easy enough to use a Uno to program a bootloader onto another chip. I describe this process here.

The idea of holding one chip on top of another is likely to fail for various reasons. Both chips will try to respond to the programming attempt at slightly different times, probably making them both fail to be programmed.

See my post about making a breadboard Arduino. It only takes a few wires to program the target chip.



However this isn't just "paralleling the pins" - it is using one chip to program another, in the way it is designed to do.