Install it. Click on the PowerMate to load it up. Set the first two at the top as Mouse Cursor right and then left in this order. Remove the rest of the settings. Close it.
Note: I only tested this on the Windows SDL builds. I don't have a Mac. Will not work on the Windows non-SDL builds and Linux builds. Don't forget to load up the PowerMate first before load up the SDLMAME or SDLMESS.