There is no other way than to use BlackBerry Desktop Manager software to reload the OS. It's possible that a prototype device will not accept anything but the original OS version it came with. And that will not be available from anyone except RIM. Your device is not supposed to be sold to or owned by anyone but insiders who test the units and was supposed to be turned back in to RIM.
If you can't load the currently offered public OS version, I'm sorry to say you're hosed. "Property of Research in Motion" means just that. It's their property.