Remember that all GO devices are on WAN connections, so their paths (relative to the server) cannot be set or predicted from the context of the server.
Also, FM Server cannot serve data from files not on that server.
However, why would you need to do this when you can push the data from Go to the Server?
I have the exact same need. I have a local db on an Ipad (in FMGo), and a hosted FM file on my server. From the iPad, when I have the hosted FM db open, I want it to access data from a local FM db on the iPad.
I can't think of a way to access a local file from a remote file, but you shouldn't have to. You can create a file reference in the local to the hosted, so both files become one "local" file.
...which works on the iDevice only when there is a connection.
I suspect people wanting the Server to read their local file is due to the joys of trying to "sync" data updated in the local file on the iDevice while off-line.
There are many ways to do it, and Go Zync and others have posted stuff about how to do this. Unfortunately, none of them are really simple.
We can do this with FMP just not Go
There is no fundermental as after the error message caused by a misformed reference you are asked to point the external data source manually.
As to my reasons - I have a syncronised iPad solution that despite lots of checks managed to fail sending an update when used in very poor signal conditions. I needed some data changing to encourage it to send again. Sadly the device is remote so getting the file sent back is very difficult. My solution was to run a hosted file that connected to the iPad file and poke the changes into place. I wanted to make the process idiot proof. Instead I had to talk them through manually selecting the correct file.
I intend putting in a timed graphic upload to a container to test connection speed in future so my sync will 'never fail' but I do wish FMG12 had a Get(SignalStrength) function!
I'm off to the FMG request page right now.