Kudos to you for researching ways to make your Patient more comfortable!
It has been my experience that Clozaril is sometimes the only antipsychotic effective on controlling the symptoms of schizophrenia in some Patients. Clozaril's downfall is side effects, one being agranulocytosis.
Your query, and Whispera's comment, caused me to do a little research. Excessive salivation (siallorrhea) is probably due to antagonistic action at one of the brain's receptor sites.The antagonistic action which controls psychotic symptoms at certain receptor sites also is responsible for these untoward effects. It seems that the tricyclic antidepressant, amitriptyline (Elavil) 25mg HS, is effective in controlling sialorrhea when the anticholingerics cannot be used.
Good luck to you in your endeavor. Please keep us up on your Patient's status.