The only way to get differential measurments on non-differential FieldPoint modules is to use a single channel per module.
Note: the dual channel analog modules are not isolated channel to channel and share a common between channels so they can not be used differentially. The advantage for the dual channel modules is that you only lose 1/2 of the channels per module when performing differential measurements rather than 7/8 or 15/16 of the channels.
Regards,
Aaron
LabVIEW Champion, CLA, CPI