No the Lenovo ThinkPad Compact USB Keyboard with TrackPoint(I don't mind the differences so much.) Using SharpKeys this is really easy. I do have a traditional Thinkpad keyboard non Japanse though.
All you do is press the key in the "Type Key" blank in SharpKeys.
I have actually gotten a Japanese Thinkpad keyboard for my laptop although its for the T420 model. I would have to check my Desktop to see how this works again(on a laptop right now) if you want the actual scan codes. I will say I haven't gotten this to work on Linux just Mac and Windows unfortunately.
(1) Where did you get the (internal) JP keyboard for your Thinkpad, Ebay or Lenovo parts sales?
(2) Imagine those 5 keys on your JP keyboard...
_ _ _____ _ _
|1||2||Space||4||5|
...how convenient is it for your left thumb to hit 1 and 2 and for your right thumb to hit 3 (Space), 4 and 5, each on a scale from 0 to 10? Bonus question: do you have small, medium or big hands?
And how did you get the idea to use a JP keyboard?
2) I have 2 of the 3 Japanese keys mapped to control/modifier and and the third mapped to space. Your picture seems to be off there aren't four modifier keys but three. The switch is quit seamless between a Mac and Windows. Medium Hands. I was analyzing keyboard layouts.
Just checked and you can even order from Amazon JP and let ship to Europe. Nice, problem seems to be solved. Did you ever order something from them?