The federal government doesn't control elections. You handle that at the state (or county/parish/whatever) level. At least here in Oregon, people can bring measures to the ballot by petition rather than waiting for the legislature to do anything about it, and given two party monopoly, they aren't going to do anything about it for you.
I don't think it's going to matter what party supports RCV. Once it's the law of your area, candidates will be running in an RCV election whether they supported it or not.