Yep, if you look into the source, especially the main.c, you'll see a line:
static const char ID = "GZLP01";
Means in short it will give DML the ID GZLP01 which should be booted. You can change that to what you want, let's say you have the game in "sd:/games/[GM4P01] Mario Kart Double Dash!", then you need to change that line in the main.c to:
static const char ID = "[GM4P01] Mario Kart Double Dash!";
You see the  and the  just say how many characters the ID is long. If you replaced the ID with the one you want you can simply compile it and inject it in a regular channel, if you start this channel your game boots.
Also you need to replace the line
I injected this forwarder into a wad which acts like the Disc Channel, when a NGC is inserted into the disc drive and until I started to read this thread properly, I didn't realise it was "game-specific".
thanx for the pointers on the code - just tried dols for Windwaker (default), Luigis Mansion and Doshin and all launched flawless via HBC
gotta get busy now with graphics to knock some channels together