I don't think there is an easy way to do it the only thing I can think of would be to take points on the line and get the direction to the next point rotate that direction 90 degrees and then based on that vector and the position in the list of points create a new point at a certain distance coresponding to how wide the line is there based on the line width curve. then just loop through the points in order and create a polygon to use as a collider. But again a lot of work.