Forcing digital channel discovery

Hello:
I am out in the boonies near Uxbridge. In order to get all of the digital stations near me I need two antennas one facing south and one facing north west. There is some overlap but they do get a different set of stations on each antenna. I have tried mixing the two thru a combiner but I get some cancellation of some stations.

This is fine on my ancient Sony TV. A digital scan on it is accumulative. I can scan on one antenna and then the other. I can just switch antennas when needed. It can be a problem when I want to add a station with intermittent or weak reception.

However, on my newer Panasonic TC-40DS600C it is a big problem. It's scan is not accumulative. Each time I scan it erases everything it found before. So I can have one set of stations or the other.

So question: Is there any way to force discovery of a station? I know the virtual and RF channels of the stations I want but I can't find a way to enter them directly on either TV. Are there any secret key combinations that will allow me to manually tune a new station?

Thanks!