Let the petitioners of secession carry on with their ill-guided desire to form their 'more perfect union'. Give them land, in Nebraska or Iowa, and let them have at it themselves. Let them figure out how they're going to get power, education, technology, currency, and other vital infrastructure needed to run a country. Do not send any exports to this new nation. Do not sign any international treaties with them. Detain those crossing illegally into the United States.
Maybe then they will realize the grass really isn't greener on the other side.