buy chassis bundle for its parts?

Looking through a recent offer by our VAR we noticed that a Cisco chassis bundle (chassis, sup, 2x line card) was cheaper than those two separate line cards. As we want 2 sups and 4 line cards, it would make sense to simply buy 2 chassis bundles and not use the 2nd chassis.

• is this possible parts wise? (mainly, is the bundled sup usable as a 2nd sup? I've not found if a double sup setup is actual identical sups or two complementary (but very similar, obviously) models)
• is this something that is, well, done? I can image the VAR/Cisco not allowing this particular way of getting parts cheaper.