You would need to be able to sideload signed packages in order to retrieve and rekey the roku.
Important: If there are no keys installed on your device, the Packager option will not be available. You may either generate a new set of keys or use the ReKey option on the utilities page to install keys on your device.
The “ReKey” button allows you to install a set of keys from an existing applications and use those keys to package a new application. This allows you to use the keys resident in the previous version of the application to sign the new version of the application or enable multiple boxes to sign your application. To do this you MUST have the password that was created when the keys were originally generated. It is highly recommended that you safely store the keys and password for future use. You may create a NULL application package which can be used as a container for storing a set of keys for future use. You may create a NULL application package which can be used as a container for storing a set of keys for future use.
That being said, ROKU employees have offered to 'help' individuals on request in specific cases in the past, so why this functionality isn't available eludes me. It's not like pkg files are easily obtainable outside of the roku channel store AFAIK.
viewtopic.php?f=34&t=36435#p235910 - that implies something could be possible.