To my knowledge nobody has ever really done this with their Deck so I don't have a "standard" solution.
What you would need to do more or less is "relocate" the switch in a sense. Basically there are two "legs" on the keyswitch that go through the PCB and get soldered from the back. The best I can think of is to insulate these legs from the hole they are supposed to go through and then rewire them to connect to the position you want it to function as (eg. run wires from the FN switch to the ALT PCB location and vice versa). Maybe bending the legs over so they lay flush with the bottom of the plastic part of the switch, running small jumper wires from the legs to the PCB holes, and then insulating with electrical tape would be the easiest way to do it but I have never tried so I cannot say.
Also to note - as long as you do the work properly (i.e. no scratching off of the coating on the PCB to wire it that way, no using a blowtorch to turn it nice and golden brown) this would probably be covered under warranty. Not many companies will do that anymore.
I might eventually have to try this mod out just for my own curiosity.