How do you use Karabiner with a wacom pen tablet?

I can see that it is possible to check the checkbox next to PTK-640 (tablet) in the devices tab of Karabiner preferences. I then tried to map the on-screen 'radial' menus that the wacom tablet will pop-up for you at cursor position on the pressing of any of the correspondingly mapped wacom device's keys, to a keyboard button instead, but can't figure out how this can be accomplished. I thought I should still be able to achieve what I want here though because I use Wacom's system preferences to map a bunch of different on-screen menus to the 8 'express keys' that are physically on the tablet and then, I hoped, in Karabiner, map those 8 physical keys to keyboard shortcuts. Unfortunately, even though the wacom device is enabled for modification, I can't see anything that resembles any of those 8 keys in the list of available buttons in the 'From key' section when I try to set up a 'simple modification' item in Karabiner. So how can I configure Karabiner to open various on-screen menus on a Watcom tablet? I'm running Mac OS High Sierra 10.13.6, and Karabiner Elements version 12.9.0 . Efforts thus far to resolve this are as described, I've found and enabled the Tablet in the listed devices for modification, beyond that and some googling, I've run out of ideas.