you can use the scaleX.
mc.scaleX = .5; //here your mc width will be reduced (mc.width/2)
how many pixel you are considaring as a single point, that number /2
slidePoint = 10; // user move the cursor 10px then my coluclation is 1
mc.width = 1000;
mc.scaleX = .5; // mc.width/2
slidePoint = slidePoint/2 // my scaleX = .5 so my slidePoint = 5;
I think it will helpfull to you and sorry for my bad english.