Customizing a theme in different ways for different sites on Multisite

[NandoJourneyman]

Hey guys. I've been exploring WordPress Multisite and have run into a situation that is all too common:
Since themes CSS are edited at the network level, and not at the individual website level, that means a change in the CSS will reflect along all sites in the network using the same child theme.

If I want to use the same theme in more than one site, which would be the best ways to get around this limitation? I only have ideas (haven't tried yet) and though this is a good discussion to have.

1.st idea: Create a copy of the child theme and modify for the exclusive use of a particular site or group of sites. I.E. news-site-1, news=site-2, etc. A couple of issues:

• I'm concerned this may be a violation of StudioPress licensing. Is it?
• It can get tedious real quick.
• Afraid upgrades can become an issue. Think they will?

2.nd idea: Create a copy of the CSS for each particular site. Main concern:

• Since Multisite is really only one WP installation, where do I put this child CSS? How do I make this work?

nth ideas: Your ideas or solutions are so very welcome.