You might get somewhere with this thread:
http://forum.bodybuilding.com/showthread.php?t=130833463&page=1 You'd probably have to join that forum just to ask how the reset was achieved in the end.
Apart from quaxo's great suggestions, it might also be worth opening up the case to see if there's a lithium battery that can be removed/unsoldered from the motherboard. Potentially that might be enough to factory reset - it certainly would have worked on many first and second generation PDAs.