Sometimes you have to treat the whine as a bark. Any sound your pup makes after you provide the command. Make a HUGE deal out of if. Make him really excited when he makes a noise.
My GSD would only whine as well. He figured it out and barks now when asked.
Hondo Von Dopplet L Bauernhof "Hondo"- GSD
Lilie's Tug McGraw "Tug" - Golden Retriever
Maggie - Mini Dachshund (Rescue)
Lonestar Pivo - Texas Blue Lacy
Ashe - Barn Cat
Katie / APHA