I have been working on a prototype for doing function point counting for user stories. I plan to publish in the VS Gallery as soon as I work out some quirks. The objective is to allow teams to experiment with comparing the usage of function points with the usual user story estimating method using various fuzzy metrics such as T-shirt sizing and Fibonacci series.

March 20th Update: I have been using as a reference the excellent Master of Science Thesis article by Kirsten Ribu: Estimating Object-Oriented Software Projects with Use Cases, which not only has the mechanics well explained but also a great review of prior art.