I think maybe you might be going about it the wrong way [no offence intended].
No need to take anything out in Photoshop.
Try this: Render your person in Vue with no ground, save the picture as a png and tick embed Alpha information. This will give you a picture of your person without any background at all, i.e. just your person.
Load an Alpha plane into Vue and attach the afore mentioned png image of your person to it and tick "billboard"
You will now have a person with a transparent background that you can position anywhere in your scene, other background image that will always face the camera.
This can be done using 2 billboard alpha planes for what you want, one for your background and one for your person, this makes your person independent of the background but also part of it because the person plane is transparent and all you see is the person.
hope that's close to waht you were after.

Injustice will be avenged.
Cofiwch Dryweryn.