Is there a way to prevent a region from collapsing?

I need to use regions, but users are not allowed to expand them.
Not with double click or anything else.

I've tried the following:
private void txtExpression_MouseDoubleClick(object sender, MouseEventArgs e)
{
txtExpression.Document.Outlining.RootNode.CollapseDescendants();
}

The problem with this approach is that the user actually sees the region being expanded and collapse.
Is there another way to accomplish that? or maybe a way to tell the control to freeze its painting during the MouseDoubleClick event... ?

Thanks,