Pay to Blog/Post

I am running into some trouble limiting blogging/posting capabilities to only paying members of my mu install. I tried the pay to blog plugin, but actuallly like the fuller feature set of the Supporter plugin. In both cases, the pay to blog functionality makes the link to post.php disappear from the sidebar, BUT the new post button in the top is still available and they are also able to blog via the quickpress on the dashboard.

I need to be able to completely lock down the ability to blog if they don't pay and I can't/don't want to edit core files. Am I missing something here? I know these are the plugins that are being used in other pay to blog sites, so it has to work somehow.

I do have supporter-write.php in the mu-plugins folder (which I think is the file that affects this functionality).

Thanks.