Asking the user would require a change to how SDC works.
Once your skins have been migrated you are free to change those registy keys to point to any folder. Though it is very important that all users have read write permissions on that folder.
Dear Mr. Banfield,
And it's a pleasure I'm quoting you, because I know who you are, but that's my point:
I'm all sat here. I've done all the registry changes and it's working pretty good for me right now. I could give up here but the problem is I'm an old programmer, since 1977 I'm dealing with comps, I've got my first PC (it wasn't called a PC yet) in 1979. In 1982... well, I've could told you a longer and boring history, but not!
I'm gonna repeat myself: please, just create an option, for us XP users, to choose where our skins will be, or to let us not to move them. Whatever, it was a great pleasure to talk to you, or to quote you anyway...