I tried something new yesterday at SJU and MIA... put paper clips in my passport so the only page that could be accessed without removing the paper clips would be my picture page. I used the oversized ones, put in carefully so as to not damage any pages/visas. One paper clip for every 15 pages, overlapping one page each time.
It worked, no thumbing through pages, no secondary, not even a second look.
I think I'll borrow your idea clipping the pages so that only the cover page can be seen. My original passport is full, I have an extra pages insert, and even that is starting to get filled up.
Too often a TSA screener will start flipping through the pages looking for the cover and then starts looking at the stamps. I've had other TSO's sit and flip through all of the stamps and one even remarked, "Gee, what are those postage stamp looking things in your passport?" ....
A small paperclip it is...