I think about this a lot, but I've never seen this concept. So, here's an AU where Light fails to kill Higuchi because L notices strange behavior in the helicopter. L realizes something is going on when Light holds the Death Note, and that becomes the reason to lock Light away for a while. But this time, he doesn't just sit in a room; he sees L once a day. And he's obviously forced to touch the Death Note every time this meeting begins. You might say, "So what?" And I'll say, "Imagine losing and gaining huge chunks of memories every day. How quickly would Light go crazy from that?" Plus, he'll obviously try to cheat his way out, and also convince L that he's not Kira. But it's hard to prove that after you touch the Death Note and scream, right? L begins to see a huge difference between Light and Kira and distrusts BOTH of them.
Eventually, Light probably gets used to this testing. Now, when L gives him the Death Note, Light doesn't scream. After gaining his memories, he pretends nothing changed, but L sits there with a sly expression, like, "Oh, no, I see"-
"We're wasting our time here. Can't you see I'm not Kira?"
And
"We're wasting our time. Can't you see?"
