Thank you for contacting us here at the answer forum. That is a very good question and I would be more than happy to answer that for you. The only slingbox still for sale that would let acomplish this would be the Pro HD. You could use the coaxial cable connection to watch on channel and have your cable box on another coaxial cable. The 500 and the 350 are built to take over the cable box streaming and letting you use all the features of that slingbox.
Hope this helps,
Sling Moderation Team