Rebind Mouse 4 as middle mouse, is it possible?

I use this 3d app called blender, and in blender the middle mouse button is used for many operations. One such operation is being able to pan the view by holding down middle mouse and dragging the mouse around. I would like to rebind my side mouse button (button 4) as my middle mouse button. I have tried setting this up in btt (mouse4 -> middle mouse) however this seems to send a single click. The remapping that I would like is for the middle mouse button to be pressed down as long as my mouse4 is pressed down. Is this possible with btt?