As of this PR, this functionality has been added into SM 1.11 (and this PR changed the function name to be the same as this). Since this functionality now exists, this plugin will no longer be updated / actively watched for PRs for those who want to stay on SM 1.10 once SM 1.11 is officially released.
The right way to set the collision group in CS:S/CS:GO (and TF2).
The typical way to set collision groups through SourcePawn is through SetEntData(), but that leads to the "Physics Mayhem" bug where guns and other entities could fall through the map. Instead of changing the member variable directly (m_CollisionGroup), we can just call a function within the game itself. This plugin does this for you.
If you would like to add the functionality for other games, feel free to open a Pull Request and I will accept it. Currently, it only works for CS:S on Linux and Windows.