If I was President of Mexico, I would agree to meet with him.
Act as if the meeting was going to be cordial.
And then blast the orange-haired clown on camera with the entire media present and the entire world watching.
Awkward, but extremely effective.
I think doing such a thing would be too risky, since it would potentially engender sympathy in some parts of the media and make Trump look like the even-tempered statesman in the room. Peņa Nieto should and probably will treat Trump like any other potential president, even though he obviously doesn't deserve it.