How can I add channels without running a scan? or even just manually tune to a channel not in the scan list?

Not all the transmitters are in the same direction so the antenna has to be pointed different for different channels. It is not feasible to rescan every time I change channels. It would be fine if you could scan and only add new channels, but instead it deletes all previous channels every scan.

Omni-directional antenna won't work, signal isn't strong enough.