I too thought about this as well. But how much longer? 10 miles, 100 miles, - 1,000 miles ?Keep in mind that you are trying to seat a new pad on worn roter face, this will take longer than if the roters han been resurfaced. Imo brake roters should allways be machined or replaced when changing pads for the best performance. Good luck!
With non-resurfaced rotors w/ 20K previous miles, I would think that ~120 miles would be long enough.