Actually batteries usually provide more than 1.5 when fresh, so running the keyboard on 5v would be find I would presume. And as for the insides, I doubt there are the USB - and + lines in there, or at least easily marked. Usually your keyboard will have a controller chip that is connected to the grid of buttons, and will interpret those button presses and will convert them to USB data and send them out over USB, on this wireless one, USB isn't needed, it probably sends the keystroke data in something like I2C or something to the wireless chip and that will "wireless-ize" the keystrokes. There probably isn't any USB bus inside of the keyboard. Your best bet would be to somehow find and purchase a wireless receiver, but the thing is, is that usually with wireless keyboards (unless their Bluetooth) the keyboard and the receiver are "married" meaning that you can not mix and match keyboards and receivers.
Imagine if all of the receivers were the same, if there were 2 wireless keyboards in range, the receiver would get both of their keystrokes, so to defeat that (and to defeat wireless sniffing of the keystrokes) there is some type of encryption that goes on so that only 1 receiver and 1 keyboard will work together.
Can't hurt to open up the keyboard and take some pictures of the circuit board and post them, you never know, there could be the USB data points in there somewhere.
