The client I am working with has a frameset like so...
I'm not certain about the block plugin, but can't you get hold of the relevant frame and manipulate it using the "frame tree", something like this: (from within importantFrame.htm)
parent.theFrame.someProperty = someValue;
eg:
parent.theFrame.location.href='anotherPage.html';
From what I've been reading, you might need Jquery on the target page, but you could try something like:
parent.theFrame.block();
or maybe:
$('#theFrame').block();