As stated in the topic header I'd like to be able to build account limitations based on custom properties.
You can do this today using the Account Limitation Builder app on your NPM server. You just need to add an entry for the custom property you want to be able to leverage for account limitations.
The app is in Start > Programs > SolarWinds Orion > Grouping and Access Control > "Account Limitation Builder"
That did the trick. Thanks for your response! I don't seem to be able to remove this request. If someone with admin powers happens to wander by please feel free to remove it.