Environment substitution within the drone.yml file

Is there anyway to do environment substitution with the drone.yml?
Or if this functionality already exists could someone explain how it works?

For example lets take a look at workspace section
workspace:
base: $HOME/some_folder
path: $HOME/some_folder

If this is set within the yml file it seems this doesn’t work and tries to do literal $HOME

Is this correct or are my observations wrong?