object around the path in OpenSCAD

I want to create a 3D object in OpenSCAD, which is a projection of 3D object "travelling" around the 2D shape. E.g. I have this 2D object:

  hull() {
    circle(r=3);
    translate([0,35,0]) circle(r=3);
    translate([10,0,0]) circle(r=3);
    translate([10,35,0]) circle(r=3);
    }

And I want to have a sphere travelling around its outline. When I use minkowski() transformation, I get not only the path of the sphere filled, but whole area inside the path.

I want this https://en.wikibooks.org/wiki/File:Openscad_rotext_03.jpg as a result, but along the hull object.

So, something like this? To get a hollow output from minkowski(), you have to supply a hollow input, rather than a complete rounded rectange. Ideally this would be a 1-dimensional space curve, but since OpenSCAD doesn't support anything like that, we can approximate it by subtracting two slightly different-sized versions of the rectangle.

$fa=0.5; $fs=0.5;

module shape(r) {
    linear_extrude(0.01)
        hull() {
            circle(r=r);
            translate([0,35,0]) circle(r=r);
            translate([10,0,0]) circle(r=r);
            translate([10,35,0]) circle(r=r);
        }
}

minkowski() {
    difference() {
        shape(3);
        shape(2.99);
    }
    sphere(2);
}