I don't quite get it. Set mp_allowgaussjump to 1 and it works perfectly.
You don't need a plugin for it.
"I realize gauss jumping can be enabled in HL by default. But it doesn't seem to work very well."
It works, but not in Single Player mode. If you start your game through console
command "map stadium3" SP mode will be activated, which works different from
when you start a game through "Create Game" option or create a dedicated server.
In both cases, however, the CVar will be set according to maps\mapname.cfg's
entry on the CVar, even if it is not visible to you in SP mode. Probably a code
leftover since in HL1 SP gauss jump was off by default.
So, you will only need this plugin if you load a map in SP mode and want to force
the map to have it enabled/disabled.
: I take back everything I said. Seems the option to alter it mid-game has been removed to
save people from their own stupidity. What happens? They create a plugin to workaround it.