Hi Galson,
I think the way to do what you are looking for is to write to Network Published Shared Variables on your FieldPoint controllers. Then on other systems you can read these variables, and if there is no new data on the variable, it will simply read the last value it read. There is no way to use a FieldPoint read that is not connected to anything without getting an error.
As far as ensuring that the shared variable will still be available, you can host all of your variables on your local PC. Then, a FieldPoint that is offline will not take the variables offline as well.
Regards,
Stephen S.
National Instruments
Applications Engineering