This is one way.
Once you dog understands the concept you play puppy baseball. Have the dog sit at the pitchers mound. Drop a bunch of bumpers on first base then walk back to home plate . From home plate toss a bumper to first base to get your sitting do to look that way then release the dog with your hand signal and verbal cue such as "over". The dog should run to first base pick up a bumper and deliver it to you. Repeat until you no longer have to toss the bumper to first as he has learned to pile. Take a break for the day then teach 3rd base same method the next day. Second base is a little tricker when you toss the bumper to second toss it over the dogs shoulder on the direction you want him to spin to and use a different verbal cue such as "back" to help him understand you want him to go back rather than over. Sorry hard to explain on my iPad but search the internet as I'm sure there are much better explanations. Once the dog has learned all three bases then you can make it a game by giving pup a right over, left back,right back, left over in any combination.