Getting odometer reading from a car with a digital dash at the junkyard

Exactly how does one do this? Even if I could get a battery in the car, is there a way to get the odometer reading from a car with a digital dash with no ignition key (like pressing a button). Rumor has it that pressing the trip reset button might work, but I'm also wondering if there might be a trick to it of if this is even true. Is beats trying to splice wires.