Is it possible? Ideally I'd like to set up some sort of WASD control scheme rather than use the mouse for everything.

Keyboard movement is already possible by default, although it involves seven keys (WASDZXC) rather than four.

One problem with the keymapper is that it literally remaps keys, so if you remapped letter keys and try to write down notes your letters will be all mixed up. DOSBox has no way of knowing whether your in "movement mode" or "map mode".

It's best to just use the game's default controls, they are similar to modern WASD: use S to walk forward, W to run forward (rarely needed), A and D to turn left/right, Z and C to strafe left/right and X to move backwards. it's just like WASD but one row lower.