One thing that disappointed me about the 777 was that only livery had the Cabin. I don't fly KLM much. So I did a little experimenting and discovered a way to add it to all the liveries. Keep in mind if you do this the VC will no longer be available.
It's a simple edit to a CFG file.

So this is what you do, go to FSX root\SimObjects\Airplanes\CS_B777-200ER_GE\model.200ER_GE then open the model.cfg file. MAKE A BACKUP!

Go to the "interior" entry and delete that and add this in

[code]..\..\CS_B777_PAX\model\csx772_pax_interior[/code]

Save then close.

Then go to FSX Root\SimObjects\AirplanesCS_B777_PAX\texture

Select everything in there then press ctrl+c then go to the variation of the 777 you edited and open up the texture folder and press ctrl+v.

That's it.
Don't forget to copy the textures or you'll have a black interior.

I just used the GE version as an example. It can be used on any of them.

As a final note, make sure the folder you copy the textures from just says "texture" not the livery folders. The "texture" folder is the folder that contains VC textures in CS planes.