That is a good idea. I think the roller may reduce effort a little due to the added travel the cable must take for the same pull distance. Make sure you put the old cable tower back in the block to keep out water and dirt. A bit of grease in there is also advised.
P.S. I tried pieces of heater hose on my mounts too. Made the vibrations worse. If you find vibration a problem, start with going back to solid mounts. Another large source of vibration for me was the cheap kit chain and sprocket. A quality chain will help alot and a custom rear sprocket will take care of the rest.