It should be possible without problem (as it works here)
- under "Game port" , "port 2"
-- (1st drop down) select "custom 1"
-- (3rd drop down) select the controler (joystick, pad, etc.)
-- click "remap/test"
- select 1st line and click on remap
-- press the wanted key to set
edit: oups... should have refreshed the page as another answer was provided
