If you have a trusted third party that can hold content for you, why not just have them store the actual data? Unless of course it's very large, but that seems unlikely to be the case in this scenario.
You could actually have quite a lot of data generated in a lab, depending on what you do. By only storing the signatures, you can have a much cheaper service that what would be needed to store GB of data, and really focus on other aspects that are critical for this: security, backup, user interface, speed,... Having only to worry about backup of a bunch of signatures is a much easier task than having to worry about backing up the actual data.