Pup dropping Bumper on retrieve

I have a wee problem that's developing and hopefully some of the experienced handlers might quickly steer me in the right direction, with a wee bit of advise before it gets it gets to be a real problem - and its engrained to deeply.
My 5 month old Drahthaar lately during both land and water retrieval, he's dropping the dummy at either the waters edge, or before me - before I can take it from him. General manners and the command to sit is going good - but it's proving difficult to enforce when he's got something in his gob! Other facets of the training is going great, and so far he's been an easy dog to get the message across to. Research I've done on the matter has unveiled all sorts of remedies and methods to correct this, but as he's only 5 months (22KG) I'm consciously aware not to put un-necessary pressure on a young dog.
I know this developing problem can be a real pain in the ass later down the track and difficult to correct - hence my keenness to nip it in the butt now. I also know problems are caused - not necessary inherited. All through - I've not been in any hurry to take what ever he's retrieved and let him hold it for a while with praise before I've given the command to "Give" Not sure where "I've gone wrong" and any suggestions would be greatfully appreciated.

Cheers Grant

Stop doing retrieves for a while then go back to the start.
Make pup sit by you. Get him to hold the bumper in his mouth. Then give the command "give" and take the bumper from him. Then go through all the progression of longer time and further distance.
If he puts the bumper you could try turning and walking away. The pup will probably pick up the bumper and follow you.