Found it!

With the help of Kylia on the McShepSlash yahoo group, we now have the SGA/Die Hard 4 fusion fic:

Live Free or Die: The SGA Fusion

Author: sian1359

Pairing: McShep
Category: Action/Adventure; H/C; AU
Rating: Adults recommended because of violence and language
Word Count: ~44,000

Disclaimer: Characters and Storyline -- Not Mine

Spoilers: Severe for the LFDH movie and character deaths that have taken place during Seasons 1-4 of SGA

This past weekend was action movie weekend.

My housemate and I rented three DVDs from Blockbuster, and out of the three, one is relatively new (Hancock) and the others I had read as Stargate:Atlantis fanfic. Now, the two movies were "The Librarian: Quest for the Spear" and "Live Free or Die Hard." We will have to wait for the fic link for the second, as it is currently not anywhere to be found. So I've included a little random bonus.

I Don't Do Floors (The Rest is Negotiable) by danceswithgary [PG-13]

Summary: "So, do you always travel with a machete and a parachute?" SG-1/SGA AU remix of 'The Librarian: Quest for the Spear'.

Categories: Slash Pairings > McKay/Sheppard
Characters: John Sheppard, Other, Rodney McKay
Genres: Action/Adventure, AU - Alternate Universe, Humour, Pre-slash
Warnings: None
Chapters: 1 [Table of Contents]
Series: None
Word count: 15120; Completed: Yes

Stuck on You by darsynia [G]

Summary: "Isn't that just typical," Chipped muttered to himself. Then, a little louder, he said, "You don't have much room to talk--at least I don't have a *mutant edge*. I thought there were regulations against that sort of thing."
((They're ICE CUBES. *headdesk*))

Categories: Slash Pairings > McKay/Sheppard
Characters: John Sheppard, Rodney McKay
Genres: AU - Alternate Universe, Humour
Warnings: None
Chapters: 1 [Table of Contents]
Series: None
Word count: 1407; Completed: Yes

I will continue to look for the die hard fusion fic. Wish me luck!