I just found this PDF online:
The Effect of the Integrated Keyword Method on Vocabulary Retention and Motivation by Joern Hauptmann:
I attempt in this thesis to close this gap by providing empirical data on how effective both methods are (cf. Ch. 9). The wider aim is to give a coherent view of the concept of the mnemonic Keyword Method with all its facets, including its possible effect on motivation. From this emerge several specific research questions.
I haven’t had time to read it yet, but thought people might be interested.