Yes, I know about the Kel-Tec one round extension. In fact, there is one in my spare parts box.
However, there may be a better way. I just installed the contents of the package I ordered from MagGuts | The Last Round's On Us!
The promise is an extra round without any extension of the magazine's length. After installing the parts as described in their instructional video, it seems to work while hand cycling. Tomorrow at the range will be the real test.
Look for results here soon.