Javascript events contain both a key "code" (which generally corresponds to the position on the keyboard and/or the function of the key) and a character string which represents the text that should be added to e.g. an input box.
It seems this game appears to be using the text string to decode the key, so I can press shift+7 (the same key I press to get a "/" character) to trigger the right flipper. You can press whatever key-combination you use to get a "/" character and it will likely work as well.
That is lucky (many things use the code which can be hit-or-miss) in that we can trigger the right flipper, but, at least for me it is a very awkward gesture.
I think it would be nice to be able to change the player controls. I seem to recall the original game permitted this, but the menu option in this version doesn't seem to do anything except pause the game.
I don't have a key for the forward slash either and still am able to write it: /////
The trick is that people like us can reach it by pressing Shift+7. Which of course is rarely recognized by games (or IDEs for that matter - many shortcuts simply don't work).
On my swedish keyboard the left bumper is z and the right bumpers is the *-key (right of 'ä'). Tilt is still x and . so no tilt proximity for the right bumper but usable.
Apparently these are used regardless of keyboard layout.