Start your session with having the bumper at his/her level and gradually lower the bumper to the ground. For some reason it is difficult for a dog to get the "concept" of picking it up from the ground so: rest part of the bumper on your foot with your hand holding the bumper. Then have your hand near the bumper without touching it and gradually increase the distance of your hand touching the bumper. What ever you do take your time and make a little progress at each session. Each time you have a failure just return to fetch from the front, you will get there!
Both are good suggestions. Progress slowly, inch by inch and day by day. The next hard one is convincing the dog that it can actually walk withe the bumper. They will retrieve it when thrown, but. Pick it up and walk with it.... It all comes togetjher in the end, but some take days/weeks longer for the light bulb to go on.
