Since COSMOL can work with NURBS splines as noted here, I would create the shape with splines rather than a polyline with a lot of short segments.
I would start by creating a few reference lines for the vertical line of symmetry, and horizontal lines at the top of the two curves to be used to define the horizontal slope of the spline at those points. Use a polyline for the straight segments (green) and 4 or 5 fit points for the curves (cyan). The fit points I used are the blue grips you see highlighted. Use the T (tangency) option for the end of the spline and use osnap nearest to ensure the slop is horizontal. Do not worry at this stage that the spline does not perfectly match the desired shappe.
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Now select the spline a zoom into the area that does not have a good match and in the properties box change the Method from Fit to Control Vertices and the spline will show its CV points.
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Click and drag a CV to get a better match. Below I've moved the 2nd CV.
Edit the spline CVs as necessary and then mirror the splines and polyline. Keep in mind that you get smoother curves with as few CV's as possible but if you need more local control of the spline's shape feel free to add additional CV's with the splinedit command. You should find that you can get a pretty good fit in a few minutes. Finish by using splinedit to join all the splines and polylines into one spline.
lee.minardi