The original poster got it right with his use of the phrase "Runway ID",
because it is, in fact, an ID based on a number, as opposed to some type of
number.

What is the magnetic heading of Runway 5?

If someone is named "Fred", do you refer to them as "Zero Fred"?

The point is, we are dealing with a "name" which consists of a numeral, as
opposed to an actual number.

The runway is NAMED Runway 5. Why would you prepend a zero to a NAME?