Originally Posted by
veganbikes
Yes you could use the wrong shifter and make it work. Would I, no especially when the proper shifter exists. The reason you DON'T use the wrong shifter is you have to lock out so it doesn't make that third shift which most people would know would go outside of the cranks which is bad and overtime you are likely to break that lock out and you have the problem. Yes you could tell someone hey your shifter has three shifts (or five with trim) but don't use that third shift and guess what someone will forget make a mistake or maybe a mechanic could screw it up not knowing or not noticing. It is simply not worth it personally to recommend incorrect parts except in an absolute emergency but this is not one of those times.
An alternative to the method you describe is to click the lever once and then set the
small ring stop to that; this way the last click is the last click and no worries about stressing the ratchet, etc. Because it is the front mech spring that is exerting force on the inner stop in this method the rider doesn't have to consciously avoid any lever positions. I have done several bikes over they years this way and have
never seen a failure of shifter or front mech.