Originally Posted by srestrepo

you can replace the shifter or as mentioned above set the derailleur to the middle or big gear. the easiest way i can think to do this is by using the limiting screws so that the derailleur is fixed is the middle position. make sure when you do this that you shift through all of your gears in the rear so that you can tell if the chain will rub and make teh adjustments as necessary.

good luck