blockUI triggers "non-secure items" warning on https pages in IE7

[fbuchinger]

I am using blockUI in an intranet web app that is accessed via https. Internet Explorer 7 displays a "this page contains secure and non-secure items warning" as soon as blockUI starts blocking the page.

This seems to be caused by the dynamically generated <iframe src="javascript:false;></iframe>" that blockUI creates to do its work. This article warns that IE7 is very picky about iframe sources when the page was served over https.

Is there a workaround for this?