You can use DropBox to send a file and even write a script to save a copy into Dropbox either when you close the file or by button, etc. Your employees can the open Dropbox, select the file and have it open in Filemaker Go. This will not overwrite the file but add a file with a numbered copy so they should delete the file on their device first.
So, make a file with just your customer data and then have the other files link to it. The new file will link automatically.
Also check out GoZync by seedcode which helps syncronize remote files with your main computer or server.