Yep. All you have to do is move the clock back to a time before the launch of Leopard.
But there are side effects. ? Yes. For example when using safari and you try to type a website, safari will no longer give you a few options of sites or fill in the website automatically, nor will it fill out forms, or usernames and passwords on sites. This is because MacOS X will not have any records for the new time u set. Other programs are affected too.
Is this bad. No just an inconvenience. And I think if u install windows then change the time in OS X to the present, your windows partition will not work unless you change the time back.
Thats it just an inconvenience. But really, with Snow Leopard around the corner you guys can wait.