Cable & Satellite TV → [DIRECTV] "Spliting" A Single HD Feed

I have an off-air antenna and the oval three-LNB dish, multiplexed on the roof so a single cable feeds my living room. I now have the 10-250 HD TiVo with two tuners. Is there any way that I can easily "split" (I know that is the wrong term) the single satellite cable feed into two and then use the two new outputs to connect to the two tuners? I called DirecTV and they said the only way is to run another cable from the mutlplexer on the roof. That is not practical because of the cable would need to run through the ceiling and an internal wall. Thanks for any help or insight you can offer.

can't do it without a diplexer (i think that's what they call it).

Thanks but I need a more detailed explanation. I'm not the sharpest tool in the drawer.

To use the other tuner, you have to run another cable. A splitter, diplexer, or another multiswitch won't work.

From another forum, »www.tivocommunity.com

A diplexer is a special kind of combiner/splitter. It combines the OTA frequencies with the sat frequencies and then another one is used to separate them.

The only way is to run another cable.

I actually meant a stacker/destacker in my original reply. A diplexer is something else, and as Balzer stated, will not work to split the signal. A stacker/destacker system would be needed and can be a bit complex to setup not to mention expensive.
Here's an example: »www.9thtee.com/dssstuff.htm

A stacked system will NOT work with the triplesat dishes. His only option is to run a second cable from the dish.