problem to moving 3d objects in 2d scene

[Víctor Paredes]

I'm chilean and this don't allow me to write in a very very nice wonderful English.
Anyway... I have a problem with the 3d objects:
I'm working in 2d but I want that some objects be in 3d. For example, the body of the pictures is a 2d picture and the head is a 3d object that I made in Wings3d. I don't like the fill which moho puts in the 3d object, so I draw it by myself using vectors and I put tha over the 3d objects (and in this way, the objects seem to be 2d). The problem is that when i move the complete character, the fills don't fit with the 3d object.

I think this happens because the perspective changes with the position of the object in relation with the camera.

Can I make that the camera doesn't do this?