If you have a boolean parameter, you should consider having two variants of the function instead. Having a boolean in the parameter doesn't help the user to read the code. To avoid duplication the actual implementation may contain a function with a boolean parameter but it can be hidden from the user of the API.
getSomeActive("foo")
getSomePassive("foo")
Another alternative is two use meaningful flags e.g. an enumeration instead of a boolean.
getSome("foo", FetchStyle.ACTIVE)
getSome("foo", FetchStyle.PASSIVE)
And to answer your question: having to declaring an extra variable for clarity just tells us that we have a problem in the interface. If you cannot alter the interface or wrap it then a variable is one way to document the intent. Unfortunately, someone else will probably just refactor the code and remove the variable at some later date.
Reference: Tip #12 in Clean Code by Uncle Bob