That's what I was thinking. Don't need fancy graphics, just make the back button work further back than the tab creation. Doesn't even have to be a copy, if they make the history a tree structure in memory.
From a user perspective, my main pain point is the prior history running out at the point where I opened a new tab. In many cases I've already closed the tab it came from, and if it's not closed I have to go looking for it.
Are there any disadvantages to this approach?