Film the subject against a black screen. (Film with a different tape than the one you're currently using.) Then play the tape on TV and set the camera (with the real tape) to film the video screen. This'll add the video strobing and noise to make it look more like a video projection. Then take the video into Premiere, and superimpose the hologram character into the background scene using the "screen" command. (I've tried, but chromakey and lumakey just don't work. Screen actually makes the subject slightly tranparent.) Then dub in sound, and there you go! Also, before you superimpose, add a filter to give the holo-character a bluish tint. That helps.
OR, TO BE A LITTLE MORE SPECIFIC:
Film your talent infront of a Black screen. Velvet is best becasue it's the blackest material out there.
Once you have this, import in into Premere and make it a filmstrip. Take it into Photoshop and reduce it to a greyscale.
Make another layer that is your prefered tinge of blue. Use the Overlay transperencie on the blue so it is transperent to the greyscale filmstrip underneath. Now your talent will be Blue or whatever color you want.
To give it that holographic look, your going to add scanlines. Make another layer and alternate with pure black and pure white horizontal lines every pixel down. So every pixel down will be a horizontal black line, then white, then black, etc, etc.
Give your scan lines a Soft Light transperancy and your set.
Flatten the image and save it as a filmstrip again. Now you will have a blue image with scanlines. Much like the one at the top of this message.
Take a filmstrip of your background footage, and layer the two together, (Experiment on what transperency to use). Then flatten that and send it back out to Premiere.
Additionaly, if you want to, give yourself signal interferance by making thicker scanlines that scroll down the image. (a filmstrip of an AVI) You can also use different plugins to tear and mess up the image once in a while to give it that holographic look.
To do this non-digitally, the best way would be to use glass:
Take your camera and set it up where you want it. Then take a large pane of glass and set it in front of the camera, but at an angle(vertically) to it. Then have your "hologram" stand so that he is being reflected off the glass into the camera. This will at least make him transparent, and your actors can still associate with the hologram, but make sure they're behind the glass, or to where you can't see their reflection.
