Nope.....you change the drive and the speedo will be in error.  It is a fact of life.  I have a friend that changed the sprocket sizes on his KLR and he used his GPS to place pieces of pinstriping tape on the speedo face at the 25, 35, 45, 55 and 65 numbers for reference.

Wonder why we seldom use 30, 40, 50 or 60 has speed limits?  What is wrong with even numbers?

North Hollywood speedometer might be able to fix you up with a ratio changer that inserts into the cable.  They are used on cars and trucks that change transmissions or run different tire sizes.  They are a bit bulky and I have never seen one uses on a motorcycle.