Sounds like Fritz Kreisler, though generally the composers he "credited" were one or two notches down from Mozart and (J S) Bach -- Vivaldi, Boccherini, Couperin, W F Bach, Tartini, Pugnani, etc. You can find a list by going to http://en.wikipedia.org/wiki/List_of_compositions_by_Fritz_K... and searching for "falsely".

Apparently, when called on his deception he said "The name changes, the value remains".