I received an e-mail from a player trying to set up a controller on Mac and thought this might be helpful.
Yeah, general controller support can be tricky. I will look into making the setup more flexible when I update it next. The setup was based on an Xbox360 controller and that controller interpretation in SDL uses half of an axis for the trigger input. The default alternate fire is currently poorly mapped to the forward moving axis of the analog stick. For now there are a few things you can do.
The first is to press a trigger when it prompts you for an alternate fire trigger in the axis setup. This of course won't work if your controller triggers are not mapped to axis. If it doesn't work for your controller (IE it's still firing when you're moving forward), then you can edit the "settings.ini" file found next to the caster executable manually and assign a bogus axis for the alternate fire. In the sample below, I set it to 10.