Apache 2.0 -- Conditional caching of .css .js and images

[c-low]

Does anyone know how to conditionally set caching for certain files with Apache 2.0 based on whether there is a new version available?

This is the scenario:
I want my stylesheet to be cached for one week unless there is a newer version available. So if I update a css file and somebody views the site within a week of their last visit, I want to override that one week cache rule and reload the file.

As far as I can tell, I have 2 options:

ExpiresByType text/css "access plus 1 weeks"
ExpiresByType text/css "modification plus 1 weeks"

And I don’t see any option for what I need. Any help would be greatly appreciated.

Cheers