Plugin to convert current site's changes into a child theme?

A friend’s site was built on the twenty-ten theme without the use of a child theme. To avoid losing changes to the site, the theme and wordpress haven’t been updated in a very long time.

I’m wondering if there is an easy way (such as a plugin, paid or free) that will copy your current theme with all it’s changes to the code and turn it into a child theme so that they can finally update their original (parent) theme.

Any thoughts are greatly appreciated because I feel like I come across this problem quite often, recently but haven’t had luck finding something simple like a plug-in.
Thanks!