Hi Dx 2004 GBM had hiccups when on decadron the only thing that worked for me was frosting ( vanilla ). I would eat a table spoon full and the hiccups would go away for a while. I know some think that sugar is not good for Brain cancer but I have a sweet tooth and aways have, I'm still here 5 yrs later. Try it, it worked for me it may work for him.
Good Luck, Stay Strong : John