Is it possible to perform diagonal jumps in the game "Bruce Lee" using the joystick?

According to the game manual yes, it would be simply move up + left or right, but I can't get diagonal jumps emulated with DOS-Box.

It is not useful either create a button mapping , since, for example, the left diagonal jump corresponds to the "7" key and not "up" + "left". So I would have to assign a specific button for the left jump and a different one for the right one.

This is a situation that occurs in other games that also have a specific key for diagonal movements.

How do you solve it? Or is the only option to play with the keyboard?

Thanks.