You can buy a programmable macropad / keypad (there's a huge range in price). With the most programmable ones (look for "QMK"), you can assign keys to any arbitrary combination or sequence as you choose, and if required make layers, e.g. NumPad layer → IntelliJ shortcut layer → Some game shortcuts.

Just an overview: http://xahlee.info/kbd/programable_keypads.html

I think the only disadvantage is it's a separate thing, so you have two things to push away from you if you don't want to use the keyboard.