I would say no. without a radio the mp3 player has no way of making music. Even if you try to wire the headphone jack up to the speakers the mp3 player does not have enough power to Supply the speakers and would do damage to the mp3 player.
You could buy a cheap radio from a store or pawn shop and get a MP3 FM Modulator for less than $20 bucks and you’re good to go, you would still have to wire the radio up. If the wires in the dash haven't been hacked you can buy a wire harness adapter and wire the radio and then just plug it in to the factory harness. Be sure to choose the right harness for you make and model.
