The only recommendation I can make is to use a transparent plane behind your model perhaps with some kind of texture as in a combination of diffuse and 100% bumpmap (same texture as diffuse). By default Anim8or background, panorama and cubemap can only be textured as they do not support ART Attributes (transparent, glossyreflector and dielectric). Use a plain coloured background, say black (but do experiment with different colours) and use a textured transparent plane behind your model and make it big enough to exceed the Field Of View (FOV) of the camera in Scene Mode.
I hope this is what ya need to know, however in Scene mode be careful how you use lighting as anything transparent can be lit up too, but there is a way to alter the material so it's not so reflective but still noticable.
I'm not too sure if this is what you mean but IF it is then make the transparent plane somewhat(but do experiment) like thus:
Create a plane and rotate it so it is face on. Experiment with colours first as you may not want to texture it. In materials editor set transparency in the range of 0.1 to 0.5. There are other ways to create transparency nut I recommend this following link:
http://www.anim8or.com/download/preview/art_raytracer.htmlAs for the render you can also render the alpha channel for .gif transparency.