Hi @NStone ,
did not try, but the documentation says, that OS is reachable via that. So, may be you have to set an enivronmentvariable for example named ThisIsMySecret and address this with ${OS.ThisIsMySecret}
The way to set the environment depends a little bit on the system you are working on. In Powershell its as simple as

May be, this is reachable vis ${OS.X} 🙂
Hope it helps,
Christian