Here’s another question about an antique

I have a new to me Fujitsu 3400, this device has several self explanatory HotPads at the bottom of the LCD, and one programmable one. The ever helpful userguide states this about the programmable hotpad:

Programmable hotpad
This hotpad can be programmed for application-specific functions. Contact your local help desk or reseller if you need assistance using the Programmable hotpad.

Fujitsu’s FAQ on the subject is just as useful

I am sure that five years ago, having spent probably $2000 dollars on one of these things, my local retailer would probably be falling all over himself trying to please me by helping me program this hotpad, unfortunately I picked this device up recently on eBay and my local Fujitsu retailer would probably just go “Huh?” if I asked about the Stylistic 3400 hotpads.

Does any one know anything about programming the hotpad on this model?