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If you have a mouse (as opposed to a trackpad), the simplest solution would be to make a scheme that uses a part of the keyboard and the mouse, and assign it to the first player slot (first player is the one that picks the mutations).

Otherwise, you could, for example, make it so that a couple of other keys would move the cursor to where the mutation buttons are,

aimx=(D-A)-Digit1*0.44-Digit2*0.22+Digit3*0.22+Digit4*0.44

I'll include a couple of new things for control schemes in the next update.