Okay, after much hacking around I think I figured it out --
Wideserver/wideclient is required -- they must startup before FMGS.
Offset Byte Set should be used.
Offset values must be set with the 'x' prefix, e.g. 'x78ED'
Parameter values on the other hand do not have the x prefix, so for F/CTL ECAM I would type in '14' for parameter (push button pressed), and '72' for release, confirm in the dialog box.