This faking thing seems to be fairly popular. Pretty new to the scene then, let me see if I understand this correctly.
For a pair scene, you have 3 photos.
1. A face photo of the primary.
2. A face photo of the lover.
3. A picture where you insert both.
Okay ! I've done this before !
I did this for a friend of mine in Facebook and her boyfriend.
While it might be certainly possible to find sex pics where the original actors are both facing forward normally, most sex pics I've seen have the head in all kinds of angles and rarely just facing forward.
I think it would be easier to find a photo you want to fake and =THEN= based upon the head positions, take NEW photos of the people you want to place in them, making certain their heads are at the same tilt and angle of where you are inserting them, and optionally giving them facial expressions to add to the scene.
If someone can provide me with a face photo of themselves and a sex pic they want me to insert them in, I can certainly try to put the two or three together for them.
Hope This Helps !