I would say there's two options for speaking with the BKK immigration here:

1) Be straight forward and just ask. I don't think this will work. From what I've seen of Thai culture, they are very much indoctrinated in the "follow-the-process" of how tasks must be performed.

2) Try what Diplomatico advised and not use your original visa? You could simply attempt to pass through immigration without drawing attention to your visa. Perhaps the officer misses it and stamps a regular VOA into your passport. If you get "caught" simply explain your situation and be mentally prepared to have your original visa invoked...