Yes, if you learn to lunge correctly, then the horse shouldn't be working on the forehand!
If you are struggling to do this, then you probably ought to find someone who can teach you face to face, demonstrate and guide you.
The use of 'gadgets' to achieve this is as debatable as the use of draw-reins in the wrong hands. Ideally, with practice and patience, you should be able to achieve this with by lunging off a snaffle with a roller / saddle and the correct use of side reins (which actually become redundant when your horse isn't on the forehand).
