Thomas, I think your method might work, if you would introduce some impedance barrier between the output you intend to read and P2.
Could be a tri-state buffer, which you switch to high impedance before you are outputting an address on P2 (would require a free output pin).
A simple resistor might work too, but it should be just the right value. Not too low or you'll get Erik's smoke generator with the strong pullup on, not too high or you won't be able to pull the P2 input pin low enough to be a proper '0' when the weak pullup is on.