Make it something other than the original exorcism reworked as a psychological procedure. Have the real demon possess someone else, maybe in a different country, with totally new situations and characters. Rather than just giving everyone a milquetoast version of the first story.
And FWIW, while I'm a pretty big admirer of the first film, I think EXORCIST III had the freakiest imagery, specifically the camera zooming in on the headless statue and the killer running through the hospital room. Granted, the monologue scene where Pazuzu is revealed to be a steroetypically mincing old theatre queen, rambling on about "showmanship" to a near-comatose George C. Scott, could have been omitted with no harm done to the overall film.