Although it is pretty clear what you want, the motivation behind it remains mysterious, therefore without knowing the context, there is a chance to not giving you the tip you really need ( e.g: no space to fit the POT on the board/equipment? adjustment must be done just once during production stage? etc.. ). Anyway, as an ( laborious ) alternative to that, you could think on making a voltage divider with a resistor-array being each one in series with the next, but with a solder jump in parallel with all them so that you could trim the suited value just cutting ( actually melting ) the solder jumper. The drawbacks on this approach are: 1) You should hit the optimal contrast at the first try, otherwise should drop another solder there. 2) This should be done with the equipment de-energized ( the solderingiron could have some leakage current from mains).