First, its not the lying that you want to stop. Its the behavior that is causing him to create these lies. Focusing or saying don't lie, never attacks the problem.
Speaking of his behavior. Its very important to find out why he is doing what he is doing. And I would need more info to do that. I assume that this is going on at school? Does it happen only during recess and lunch? Did it happen last year? Have teachers actually seen this happening or is it being reported second hand? Has the school tried to stop it - they are required to do so. I add this because the most effective way to change any behavior is immediate reinforcement. That is one reason why your attempts have not worked very well is because they are not immediate.
It is also important to know if there has been just one child involved or many. If there are many kids who are complaining about being hit, etc. then its possible that he doesn't realize what he is doing.
Now, there are also conditions like Sensory Processing Disorder and ADHD where kids will bully and not even realize that they are doing that. Is your son having any other problems in school? How are his grades? Does he have any strong sensitivities to textures, food, sound, etc.
This link might be helpful to determine if he has something like ADHD.
http://www.additudemag.com/quiz/9/question-1.html?utm_source=eletter&utm_medium=email&utm_campaign=December#submit-answer
And this is a good one for SPD
http://www.additudemag.com/slideshow/50/slide-1.html?utm_source=eletter&utm_medium=email&utm_campaign=December
I will note that as an elementary school principal that I usually was able to stop bullying pretty easily by getting the kids together and talking about the situation and letting them know what was going to happen if it continued, etc. Thats why I think its important to get the school involved. However, if it is something like ADHD that is causing the problem (and I have seen that happen too), then solving it will take more effort - and I can also help with that (being the CL here -
http://www.medhelp.org/forums/ADD---ADHD/show/175
Hope this helps.