[kh99]

There's another way to do it: create a cssrollup xml file and put it in includes/xml. For exaample you could name it cssrollup_myproduct.xml and have contents like this:

<?xml version="1.0" encoding="ISO-8859-1"?>
<css product="my_product_id">
	<rollup name="main-rollup.css">
		<template>mycss.css</template>
	</rollup>
</css>

Then rebuild the styles (under Maintenance > General update tools). Then you don't need any extra code or plugins.

Edit: There are other rollups than 'main', so if you're really concerned about efficiency, you could determined which one you need. There is one called 'postbit' so maybe that would work for you.