|Binder clip. I should have thought of this earlier!|
I solved this problem a years ago with a small muffin fan on top of the heat sink. The fan is mounted on tiny rubber feet. It blows air upward, resulting in airflow across the fins. Placed just above the finals, it does a good job of keeping everything cool.
This fan is noisy at full speed, so I used a small resistor in series. The resulting half speed airflow is more than sufficient.
This worked great at my Gwinnett QTH for years, where the radio was raised above the desk a couple of inches by a shelf. The K2/100 sat almost flat, and the fan stayed in place. However, when I moved the K2/100 to the parsonage QTH, the radio rested on the desk, and I used the KAT100 tilt bail. Because of the tilt, the fan had a tendency to drift to the back. Every once in a while, it would fall off.
While I was readying the K2/100 for the 2020 ARRL RTTY Roundup, I wanted to make sure the fan stayed put. I came up with a very inexpensive solution. A small binder clip attaches easily to the heat sink fins. The ears of the clip rest against the fan body and prevent it from drifting.
Worked about eight hours over two days in the RTTY Roundup, and the fan never budged. I really wish I had thought of it sooner!