Getting GasLevel from IMyInventoryItem.

I would like to get GasLevel value from hydrogen bottle. I already found my bottle in a container, so I have a reference to IMyInventoryItem. IMyInventoryItem have a Content property which in this case is an instance of MyObjectBuilder_GasContainerObject. MyObjectBuilder_GasContainerObject have a GasLevel variable that I would like to read, but the type MyObjectBuilder_GasContainerObject isn't allowed in ingame scripts.
Which extensions or interfaces can I use instead?