I've been using the completely free and well written Auto Hot Key. One of the scripts allows the Joystick to be used as a mouse. With some added hotkeys using the Joystick buttons you can setup a proper control for MMB.
CODE
Joy11::
Send {Click down}; Lock down left click for one hand panning
return
Joy10::
Send {Click up}; Release left click
return
Joy6::
Send, {a down}; Zoom in
keywait Joy6
Send, {a up}
return
Joy7::
Send, {z down}; Zoom out
keywait Joy7
Send, {z up}
return
Joy8::
Send, [; Previous site
return
Joy9::
Send, ]; Next site
return
Joy5::
Send, g; Center on image
return
Joy4::
Send, h; Toggle rover tracking
return
Send {Click down}; Lock down left click for one hand panning
return
Joy10::
Send {Click up}; Release left click
return
Joy6::
Send, {a down}; Zoom in
keywait Joy6
Send, {a up}
return
Joy7::
Send, {z down}; Zoom out
keywait Joy7
Send, {z up}
return
Joy8::
Send, [; Previous site
return
Joy9::
Send, ]; Next site
return
Joy5::
Send, g; Center on image
return
Joy4::
Send, h; Toggle rover tracking
return
With a few tweaks (I needed to reduce the sensitivity of the joystick script) I now have full control over MMB. I bet the MER teams wish they could have this much live control over the rovers but I guess we'll have to wait for manned missions for that.
mouseonmars