I do not think there is any auto bone tool, but there are some enhancements to the dynamic bone tool in flash cs5.
Please look at the below link:
http://www.businessweek.com/idg/2010-05-24/flash-professional-cs5.html - search for "spring tool" in this text
Here is a tutorial on how to use the spring effect http://www.lynda.com/home/Player.aspx?lpk4=63563
Also, here is a list of new features in flash CS5
Hope this helps.