Another Suggestion...
Nuke all of the channels by selecting some local cable company's basic list, and marking them all hidden.
Set number of days to 'O'

Then add two change button function activies that re-map the FeatureUp/FeatureDown buttons (internal name for channel up/down) to send the IR command for ChannelUp / ChannelDown.

The change button function activities are specific to your configured activies and devices. As an example you could apply the mapping listed above to the 'browse all' menu under 'WatchTV' and have the IR commands sent to your TV. In effect this transfers the "keeper of the scan list" duties from the Harmony to the TV.

If you are happy with the channel scan list in your TV this should work fine. You may want to autoscan channels on the TV to get 'em all in there.