T61 standby mode different than other comps?

This is a strange problem - I need to temporarily plug my iPod radio transmitter into a computer as a power source while driving (the one for the cigarette lighter broke). I figured I would let the computer sleep or standby to use less power on my 2-hour drive everyday while using the transmitter. This works with my HP laptop, and I tested it on my boyfriend's Dell desktop, which also works. But my ThinkPad T61 (which is the computer I actually take to work and need to use as the power source) won't allow the transmitter to get power while its sleeping. Why is there a difference in the way the Lenovo stands by from the HP or Dell, and is there any way around it?