How to use a CSS StyleSheet for the aspx page on design time

Hi,
In my company we use a control that renders the <link rel="stylesheet"> tags dynamically at runtime (equivalent of scriptmanager who renders <script> tags dynamically). this control is very good, cause it select the appropriate css stylesheets depending on some criterias. The problem is that on design time for Visual Studio there is no designated CSS stylecheet since there is no <link rel="stylesheet"> tags on the page.
If I put <link rel="stylesheet"> tags on the aspx page (to indicate a design time stylesheet) this tag will be rendered to client and it causes conflicts with tags rendered by the control !
So please have you any idea about how to indicate a CSS style sheet that VS uses to display the aspx page on design time, and only on design time.
Thank you by advance,
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