embedding contents of external css stylesheet

I would like to embed the contents of an external css stylesheet at
user.head.content. That is, instead of a link to the stylesheet (a la
html.stylesheet), I would like a document-level <style> block in the
head of the document. I want to pull the css rules in from an external,
shared file, rather than hardwiring them in the stylesheet.

Anybody know how to do this? btw, the idea here is that the generated
html file can be moved around and viewed standalone - the external css
file is not always convenient.