What could work is completely recasting the character. In order to make the movie happen, which Aykroyd clearly wants, he could employ someone else to play the good doctor.
The actor-screenwriter also commented on those pesky rumors that Murray shredded his script for Ghostbusters 3.
“Bill Murray is not capable of such behavior. This is simply something that would not be in his nature. We have a deep, private personal relationship that transcends business. Bill has too much positive estimation of my writing skills to shred the work."
Who would you like to see step into Murray’s shoes as Dr. Venkman?