How to add CSS in TinyMCE editor window for plugin

Hi all,

I've created a plugin for TinyMCE under Wysiwyg. Currently I'm adding my custom CSS in mymodule_init() and that works fine for displaying the node, but the CSS doesn't make its way into the editor textarea. If I manually specify the file under the Wysiwyg options (Define CSS) then it works great, but that's not very nice. I imagine there's a simple way of adding my CSS file to the editor when my plugin's enabled?

Any ideas much appreciated.

Thanks,

Andy