Most machine shops have a little oven that we use to heat the little end of the rod.
The piston is put in a fixture with an adjustable stop for the pin. The rod is heated, laid into postition against the bottom of the pin opening of the piston. The pin is dipped in oil and then the it goes in with a light push untill it bottoms against the stop..
Doing it this way ensures the pin is centered and the piston won't be subjected to the force of pressing the pin into the rod.
The press fit is pretty tight, and substantial force can be required to install the pin.
Doing it cold can result in distorting or even cracking the piston.
In addition, the pin can get scratched/gouged as it passes thru the rod bore. Those scratches/gouges will chew up the pin bore in the piston once the engine is fired up, resulting in all sorts of problems.
We also have another fixture the pistons are laid in to press the pins out at the beginning of the machining operations. It cradles the piston, spreading the load out to minumise flattening the backside of the piston pin bore, which will increase the amount of force required to drive the pin out.
That's why it's best to let the machine shop to install/remove the pins when using press fit style pistons.
I realise that doesn't help you now, but, Muskrat has a pretty solid idea.
Quoting Muskrat:
Have you considered making a jig with a hard stop for the press?
That's good thinking right there. /ubbthreads/images/graemlins/smile.gif
Combined with a curved fixture to lay the piston in, you should be able to reposition things slightly without any major carnage.