Dashboards: Pass contextual information to external pages

We'd need the possibility to pass the current dashboard context to the external page. This works already e.g. with the session id of the currently logged in user by using a placeholder: https://localhost/?session={!$$SESSION}

see: https://experience.workfront.com/s/article/Embedding-External-Web-Pages-into-Dashboards-1487514310

So what we would need is something similar, like https://localhost/?projectID={!$$PROJECT.ID}