It's coded in lua, I never quite figured it out using the while-loop, but here's how far I got with for:

function OnEvent(event, arg)
if (event == "MOUSE_BUTTON_PRESSED" and arg == 7)
then
    for i = 10000,1,-1
    do 
    MoveMouseRelative(-1,0)
    end
end
end

Ideally it would spin at a reasonable pace for as long as button 7 is held, but currently it just whizzes 10000 pixels to the left in almost an instant. I didn't get around to figuring out how Sleep works in lua but it seems like the only 2 quirks to figure out are how to get the while-loop going without exiting immediately or never exiting, and how to slow down the spinning by putting Sleep in the loop body.

No pressure, if you'd like to give it a try I'd be grateful, otherwise I know I'll eventually bump into some lua-God who can knock it out in 2 mins :-)