Just don't try to take the easy way out with heat tape or you may create a fire hazard. Also, using a human heating pad is a fire hazard and I'm shocked your parents would even suggest it. They are only meant to be used for very short periods of time each time they are used. They often get much too hot even on a low setting if they are sandwiched between a tank and table.

Have you ever taken the cloth cover off an older human heating pad that has been used and noticed the brown marks on the plastic? Those are the burn marks. That is why most new heating pads are designed to automatically turn off after about an hour now anyway.

Until you can get properly wired flexwatt heat tape or an under tank heater designed for reptiles, I'd stick with the lamp. Just remember, no mater what you use, it needs to be controlled by a thermostat to prevent overheating and/or burns.