Of course, things are rarely that easy. I simply never could get it to work. Once I tried running it form the terminal, I could see that after its first run (once it had written out ~/.g15macro/g15macro.conf) it would segfault as soon as it was run. Bugger!
Soon enough, googling around found me plenty of links showing that the answer was to modify g15macro.c, comment out a line that was causing the crash, and hey pesto!
Being a moderately experienced Linux user, I tried to install the g15macro-dev package... nope, not found in the Ubuntu repos. OK, download source, uninstall the packaged g15macro, compile and install new version. Along the way i hit a few dependencies for the compilation:
sudo apt-get remove g15macro sudo apt-get install libg15daemon-client-dev libg15-dev libg15render-dev sudo apt-get install libfreetype6-dev libxtst-dev cd Downloads/g15macro-1.0.3/ ./configure make check sudo make install
Easy as pi, though compiling software from tarballs rather than using apt-get makes me feel like I've travelled back in time.