It's not a double penalty if the first drive-through doesn't cost you anything (you get put back where you were before doing it).
I think the problem here was you saying "until the sc...has passed," which would mean a 1 lap penalty. Waiting until the whole field (other cars behind the SC) has passed is acceptable to me.
Or, as Banshee put it to me in an IM... just do the DT/SG and fall to the back of the line once you exit.