Changing styles on the fly

Hi - possibly a bit of a weird question, but is it possible to change between GP style options on the fly? So I mean an equivalent of logging in, uploading the GP json file, but done via a hook?

End result we'd like is a public option "Change how this site looks"

I know of other ways of doing this such as creating multiple child themes, then using some kind of theme switcher plugin but if there's a better and "more generate press" kind of way, I'd be interested in hearing about it!

cheers

Mike