Hey, wow, thanks for the fics! Honestly, I wasn't even expecting a reply because I know that not many people read samifer, so thanks!
I just finished reading the first fic (yes, I have read the Fourth Wall series ^^) and you're right, it's really good (I'm totally going to go with the headcanon that Sam jumped in the last chapter D:).
Unfortunately, like you said, there arent many fics under this genre, so I can't really rec anything much for you...I'm pretty sure the ones that I have, you've already read.

Since you said that Fear of Falling was your favourite samifer fic, I would like to share mine.. I'm sure you've already read it, because it was quite popular with the Samifer fans on fanfiction.net... Stairway To Heaven (https://www.fanfiction.net/s/9065863/1/Stairway-to-Heaven) by SnarkyMuch2
Summary: AU. To save his brother, Sam makes a deal with the devil. The creature he expects and the man he actually encounters are two different beings, and soon he will have to choose between what he knows is right and what his heart desires.

If you haven't read it....Seriously, I can't begin to tell you how much I loved this fic. To date, it still remains my favourite ever Samifer fic, and I still go back and read it, because I love it so much. Like you, I was kind of depressed after finishing it because I thought I'd never be able to find another fic to compare. And I haven't so far (it's actually really depressing because the author promised us a sequel and she suddenly disappeared and hasn't come back).
Anyway..word of warning when you read it..carry a box of tissues, because you're going to need it! D:

So apart from that, like I said, I really don't have any good samifer fics in that genre. I do have two short fics, by Fightlikeagirl (actually I'd recommend all of her/his fics), but they're more to do with possessive!lucifer (who's a little bit obsessed with Sam), than a Lucifer who's actually in love with Sam.

Nothing You Do at Gunpoint (http://archiveofourown.org/works/557567?view_adult=true)
Summary: If he had any sense, he would have called the police weeks ago.

You Are The Bullet In The Chamber Of The Gun (http://archiveofourown.org/works/642189)
Summary: "You're not the Devil," Sam says, trying to sound more confident than he feels. He loathes these calls, but he's the only one Lucifer will speak to. "You're a sick, deluded murderer, Luke, you're not the Devil."

I'm pretty sure you would hav read this, but still, won't hurt :P

Break, Fill, Overfill (http://libraryofsol.livejournal.com/135453.html) by Libraryofsol is good.
Summary: Sometimes it's not about what you can see.

Apart from that, there is this other fic...but the possesiveness protectiveness that Lucifer has towards Sam is only briefly touched on and it's an eventual Sastiel fic, so I don't know how much it'll interest you. It's still a realy good read though so I'll share it with you

The Art Of Tying Bonds With Scissors (http://archiveofourown.org/works/1059499/chapters/2123227) by lysanatt
Summary: When Sam unexpectedly bonds with Lucifer, a high-ranking traditionalist alpha, Sam's beliefs about free will are put to the test. But bond or no bond: there is no way Sam will let biology get the better of him. When Castiel, Lucifer's younger brother, makes an offer that Sam literally cannot resist, Sam knows it's his chance to be free of Lucifer for good. Still, living with one mate while being unhappily tied to another is like tying bonds with scissors: it's doable, but it certainly isn't easy.

Yeah...
Anyway..again, I really appreciate the recs you gave me! Even though I wasn't much help, I hope you enjoy the fics I recced for you (if you haven't already read them)