Dang. That was quick. I might have been able to offer some stuff.
FYI, I have grown a few hamatas over the years and have noticed mine too go through a summer slump. For me, I think it is due to not giving it good highland conditions. They would pick back up in fall and winter. I got a new hamata over the summer and resorted to the cooler + ice water trick so as not to upset it too much while recovering. It's looking great and has been since I received it.
For me anyways, a cooler with an inch or two of ice water in the bottom is great for cooling my more finicky plants down in the summer time. Worth a shot if you are in a pinch during the warmer months.