Best way of adding custom CSS as part of a plugin

[Spleasure]

I am working on a plugin, and I like the new product/plugin system very much. I just need to add a couple of custom style definitions to the main CSS file, but I wonder how that can be done in the best way. I could just add it to EXTRA or EXTRA2, but then uninstall becomes difficult. Another option is to put it in a template, and load it with misc.php?do=page&template=nameoftemplate, which I also use for my javascript file. Is there an option which I have overlooked?

[edit]
The last option does not work, because FireFox doesn't like CSS files with Content-type: text/html.