Depends if it gets its power from the headunit or a built in amplifier. If it has a built in amplifier, in theory you should be able to just take the signal leads going into it and plug them into your own sub. If it is powered from the head unit then I probably wouldnt as you should never plug an amplifier into another amplifier, Unless you're sub isn't active (has its own built in amp) then thats a whole different story! : P
