Just completed co-op by myself. Those last few levels were a bitch having to use my toes or mouth to move the analog stick at the same time as using my hands to move the other one.
But, it's done, and I'm glad I did it alone, as people can piss me off very quickly and I'd rather yell at myself than a friend.
EDIT: In response to what you said about Triple Crown; The game freezes the timer as soon as you complete the puzzle, not when you enter the tube at the end. I just unlocked the achievement right after placing the ball on the button.
So just Professor Portal left.