BuddyPress.org

This has not yet been implemented. As this thread has not seen any activity for 4 months, I would suggest searching the trac and see if it was ever added as a feature request / enhancement ticket. If not, you can add it yourself!

You login to trac using your BP.org credentials.

As a side note, the reordering of groups would need to exclude the first field group as it is the grouping of fields that appear on the signup page.