I would agree that trying to sit in on what’s officially named "Transforming Ideas to Innovation " would be ideal. Sitting in a Physics/Chem/Calc class would give a feel for the largest classes he’d see, but they’re fairly standard/boring material.
A 2nd year ME course - 274-Dynamics or 263-Sophomore Design would give a feel for major-specific classes, even if the topics are too advanced to understand.
( fwiw, “Purdue” and “Current Employer=SpaceX” gives > 100 results on LinkedIn, Apple > 400, NASA/JPL >250, Tesla >150 - pretty big numbers if they don’t recruit 
)
(And I understand having your heart set on a school. CMU was my “fallback” from MIT ? . You can tell him a CMU ME grad is quite happy his kid is at Purdue ME. I really think it was a better school for her.)