Pretty sure it's just a matter of getting X220 palmrest/plastic trim surround to avoid any alterations. You can find writeups via the obvious searches, here's some such results:

https://www.thinkwiki.org/wiki/Install_Classic_Keyboard_on_x...

https://www.reddit.com/r/thinkpad/comments/9cp8pq/x230x220_k...

https://www.youtube.com/watch?v=t4_6LQrmu14