Reverse engineering fitbit data

Hack Details: I have a had a fitbit for two years now tracking my sleep, steps, heart rate etc. However I am only able to export very aggregated data even thought the underlying interval data is there (fitbit charge you to get access your data). I want to write an R script that can reverse engineer the data used to generate the graphs and create a personal database of my data.
What you need to make it happen? I can do a bit in R but help accessing an external API would be appreciated. Also someone who understands HTML would be a lot of help
Name: Paul G