As an aside, I don't know what version of FG you guys (macnab & Philosopher) are using, but if you can use the latest development code (snapshots), you'll see that there's a joystick configuration dialog available in the menu, that was recently added by Stuart.
Now, as you probably know, we also have a Nasal console available, which provides support for writing code directly in the simulator.
Both of these dialogs are conventional XML dialogs with embedded Nasal sections.
So, given that Joystick XML bindings are re-evaluated whenever their bindings are invoked, it would in fact be possible to directly write Joystick code WITHIN the simulator, by copying the Nasal editor (from the Nasal console) into the Joystick configuration dialog, and by providing an option to directly edit your bindings there, saving them to a file in $FG_HOME and reloading the bindings via an fgcommand (also available via the DEBUG menu IIRC).
In other words, by copying/pasting some stuff from the Nasal console to the Joystick Config dialog, we could be able to provide an integrated "Joystick Scripting Editor" so that people can create their bindings directly in FG.
BTW: I wouldn't be suggesting this if I didn't have the impression that the two of you (macnab & Philosopher) seem to understand the Nasal side of things pretty well already