Eagle - Custom pad shape for SMT inductor
Ok, found a way to do it. I post it here as a possible solution for anybody else who will incur in a similar problem.

I've used the polygon tool in a different way. I took the points shown in the image below as the vertices:



Then, I created the polygon with all straight lines. By editing the "curve" parameter of the segments AB and AC and by modifying slightly the position of the points A, B and C, I finally got the shape I wanted, using a circle in the tDocu layer as a reference. Here is the result and I'm pretty happy with it: not 100% precise, but it will do (for reference, tPlace tracks are 4 mils wide).