This scenario will only occur provided that there is a brokered Republican Convention.
I will assume that there is a stalemate between Cruz, Trump and Kasich. You start by rejecting all three of these candidates who have managed to destroy each other in the primaries. Then pick a set of dark horse nominees who are to the right of Hillary, but will be acceptable to moderate Republicans and many Democrats.
By rejecting all three leading Republican candidates, you will upset their supporters, but since none of them win the nomination, you can claim that none were losers and therefore the selection process was fair.
My picks for President and Vice President are John Huntsman of Utah and Susan Collins of Maine. As a past governor of Utah, Huntsman has governing experience, appears to have been successful, and was well liked. He was chosen by Obama and Clinton to be the U.S. Ambassador to China, and therefore has diplomatic experience, and clearly has the respect of these top Democrats. Collins appears competent and well respected by her colleagues in the Senate and can work with both parties. She also cannot see Russia from her front porch.
The far right wing of the Republican party will not like this choice, but because of their extreme dislike of Hillary, they will vote in droves for any Republican nominee.
You might wonder why a Democrat would propose a path for a Republican winning the White House. I will paraphrase what John Huntsman stated in replying to an idiotic remark made by Mitt Romney in 2012, chiding Huntsman for serving as Obama’s ambassador to China. Huntsman stated that his first loyalty was to his country and not to his party.