1. The Republicans nominate Trump, the Democrats nominate Hilary.
2. The anti-Trump Republicans run a pair of third party candidates, say Kasich and Cruz. They get on the ballot in Texas, Ohio, and perhaps a few other states where both major party candidates are sufficiently unpopular. They stay off the ballot in any state where their presence might help the stronger of the major party candidates, probably Clinton.
3. They get enough electoral votes so that neither Trump nor Clinton has a majority, which throws the election to Congress. The House chooses the President, the Senate the VP, from among the three leading candidates. Kasich is chosen as President, despite coming in third in both popular and electoral votes, and Cruz, or possibly Trump's running mate, becomes Vice President.