gender reveal at hospital

Ok so I am "team green" AKA hubby and I aren't finding out the baby's gender until birth... with that being said we still want a fun way to announce the gender to all of our friends on social media and hubby's family that lives out of state.
I was thinking that once in the parking lot for the drive home, we can start the engine up and have pink or blue smoke come from the tail pipe.. and record it! 
Any other ideas that may be more cute or convenient?