I would use 2 plain canvass dummies. throw one and as he comes round, encourage him closer wiht your food. As he drops the dummy, throw the second for him to fetch. Keep a mental note of how close he was to you when he dropped hte first. when he comes back with the second encourage him in again,a nd this time, he has to come an inch closer than before..if he does, throw the second dummy again. Continue over several sessions until he brings it all the way back.
Or attach a long line to the dummy so that he can't wander off with it.
Or do retrives in a narrow chanel (hallways are good) so that he cannot evade you.