Most laptops use a momentary switch like a desktop to turn on. If your soldering skills are good you could remove the panel above the keyboard (most dells have a similar panel layout/config) and solder some wires to each pin of the switch and run them to a button. Then if you needed to reverse it later, you could either desolder or just cut off the wires and replace the panel. The only real issue is that those switches are generally pretty small and you may need to remove the circuit board and solder to the bottom. Also, some laptops refuse to boot while the lid is closed, but most Dells I've seen will work while closed in a docking station. Worst case, you would have to remove the pin switch that senses the lid being closed.