How to make motion of the Sun more apparent at seconds scale?
The obvious answer is to use a telephoto lens -- or any other magnification scheme.  As an extreme example, if you had a post 1 km tall, the shadow of its top (think sundial) would move pretty clearly.  If you re-image a short post, or just re-image the sun itself, which enough magnification, you'll see the motion.  

This is kind of the same as trying to observe a celestical object with a high-power telescope. If you don't have an equatorial mount, everything in your field of view will move quite noticeablly.