I've been doing a bit more on it.  I still got a bit more work on the software side of things, but the hardware side of things didn't come out too bad. I did take some inspiration from the TV-B-Gone.  

For the MCU I decided to use the Attiny85 (attiny85v-10pu variant as that can work down to 1.8V.)  I've added things such as a small 6 pin ICSP header, an indicator LED, both a PCB mounted push button switch and some pads to use an external push button switch (great if you want to put it in a box), and a space for an external crystal.

The board can be easily put on top of a 2xAA battery back with some hot glue or mounted inside of something.