Pinout for the 2.5mm cable on the canon camera:
[http://www.instructables.com/id/Very-easy-and-simple-timelapse-controller-for-cano/]
Since I always forget that and it is kind of important:
+------+------+
| MISO | VCC |
+------+------+
| SCLK | MOSI |
+------+------+
| RST | GND |
+------+------+
MOSI is PIN 0 on the attiny45 and supposed to be connected to the RX pin of the receiving module.
"One of those supposed quick hacks that turns into a complete nightmare..." I know the feeling. I knocked up an intervalometer for a Canon DSLR a while back it was a lot of fun. I might go back to it and wireless it up. Cool project!