Your shifter options depend on the type of hub that's on your Ross, I'm guessing it's a Shimano? I've seen thumb shifters, grip shifters, and the Sturmey-style triggers for the Shimano hubs. If you want them on the down tube, you'll need to fabricate something custom.

Mounting a standard shifter in a non-standard location would look cheesy in my opinion, a bit like the seatpost-mounted brake levers that I occasionally see on budget fixie conversions, only less dangerous.