if i put resistors inside the Apple 30 pin charger can i still use it for sync? how would that connection go? can't find anything online

like d+ and d- need to be tied to a certain voltage.. can i still solder them directly to usb d+ and d- ? would that work? or should i just make a second cable as a "charging adapter" instead? i know there are cables that recognize as chargers and also work for sync and i wanna know how they do it