The only thing that *I* can think of is to do a factory reset (instructions below, from Frisco's thread). Note that ALL user data and apps on the phone will be lost, he'll have to enter his information again. However if the name and password he's forgotten is his gmail login, then that's going to be a problem because that's how Google knows him.
Pictures, music and whatever else is on the SD card will be retained.
- Shut down your device.
- While holding down both the volume-down toggle and the send or "phone" button, press the power button.
- Wait a moment, and a screen will come up: read the print completely and follow directions, it'll walk you through the simple process.