Well, many projectors have the capability to stretch the picture vertically, which would get rid of the black bars, but would also ruin the picture geometry, leaving everyone tall and skinny - that stretch mode is intended for use with anamorphic lenses, which stretch the image horizontally, restoring image geometry.
The only way to do it "right" is to replace your 16:9 screen with a 2.35:1 screen, and then use either (a) zoom method (throw the bars off the screen as you mentioned); (b) stretch mode + anamorphic lens; (c) zoom mode + "shrink method" - where you zoom to 2.35:1 size, leave the projector set that way - and then use a scaler device or HTPC to shrink 16:9 movies down to fit the screen.
Or, keep the 16:9 screen, and just accept that there will be black bars on top and bottom on cinemascope movies. You can also add masking on top and bottom to make the bars less visible / objectionable.
Edit: I reread your original post, and I think I misinterpreted - I was thinking you wanted to keep your 16:9 screen, but it sounds like you're planning on switching to a cinemascope screen, and wanted to know how you can watch 16:9 content on it without having to manually adjust zoom. See option (c) above, "shrink method".