Here is a script, 8 sets the rotation to match the rotation of the object
a/2, b/2 puts the origin of fill at the centre of the object.
pen penAttribute_1
fill fillAttribute_1
poly2_b{5} 5, 2, 0, 8, penAttribute_1, penAttribute_2,
a/2, b/2, 1, 0, 0, 1, 0,
0, 0, 1,
a, 0, 1,
a, b, 1,
0, b, 1,
0, 0, 1

the screenshot shows the parameters