For a concrete method, you can create a measure Exec Time with the method/class. This "Represents the execution time for the declared method."
So, thinking in what you want (there are several methods calls per purepath) you can calculate the times sum per purepath with a Business Transaction. You would put as filter a measure that takes all the purepaths where the method is invoked; and as result the measure Exec Time said before, with sum aggregation. With this, you would sum all the exec times of that concrete method call per purepath.
Hope this helps