How to collect all data from some distributed SQL server instances without any network between them

Hi
 
I've developed a control system for a specific industrial application. This control system uses SQL Express 2008 R2 for production data storage. There are three copies of this system which distributed in a dam project site and almost it's impossible to connect these three systems through a network, but my customer needs to have all production data of these machines in a central computer for tracking and reporting functions in a weekly manner.
I don't know the best solution for this task so let me know your ideas to solve this problem.
 
Thanks.
Amir
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