Never have. Did use atropine drops orally once for sialorrhea, but that's anticholinergic.
I'd have to look it up but I think you'd want to be careful on the selectivity of bethanechol depending on which anticholinergic sx's you were targeting.
Have one patient on it to manage the urinary retention he is experiencing from high-dose Haldol dec. Started him on 10mg t.i.d. and he's experienced relief from it.