Bypass Popup Blocker in IE7 with JavaScript emitted from Code Behind

How can we bypass the Popup Blocker in IE7 with JavaScript emitted from Code behind file? We have an image button in our application, if we used onClientClick event that contains the window.open, we are able to bypass the PopUp Blocker. HOwever, if we used OnClient click event in code behind and used RegisterStartupScript to output the window.open, the PopUp Blocker in IE7 will block the popup. If we can't achieve that from code behind file, is there any advice to achieve the same result without using mentioned approach?

Please advice.

Thanks ...