Using Engage in Blackboard

I am presently using Engage '09 to add a few interactives in a Blackboard course. I publish the Engage and get as expected the SWF, the HTML and the engage_content folder. I call this HTML from Blackboard and the Engage opens in a new browser tab and works fine.

Now my question.  To simplify content delivery for the learner I have modified the Engage provided HTML by adding a simple button to close the window once the learner has completed the interactive.

<input type="button" value="Return" onClick="window.close()">

This works fine but I get the browser pop-up asking to confirm the tab/window close. This is an unnecessary check but required by browser security. I have attempted to find a way to get around this pop-up. Security will allow close without the "Are your sure" pop-up if the window was opened with javascript. Looking at the js file in the engage_content folder it appears the window was opened as g_wndZoom.open() so it stands to reason that g_wndZoom.close() should close the window and do it without the pop-up check... IE:

<input type="button" value="Return" onClick="g_wndZoom.close()">

...but that does not work. Any suggestions would be greatly appreciated.