I played this for about 2 months with only a mouse rather successfully. He could try this out:

-Get a 5+ button mouse.
-Set Strafe left/right to buttons 3/4 (or something that is along the sides of the mouse).
-Set back up as button 5 (kinda optional, I never really did use this...)
-Set move forward as holding both buttons 1+2 (left + right click)
-Set Right click to rotate screen (I don't remember if this is default or not)
-Left Click for use of all abilities.

It takes a bit of practices but is rather effective. The most common use is to press one of the strafe buttons while holding the right click and rotate the screen to adjust the direction of your strafe. This allows for precision turning while on the move.

Note: less effective as melee dps classes...