This may be impractical but, using a StereoGraphics Z-Screen requires only that the viewer wear circularly polarized eyewear. Add a non-metallic mirror and the imaging system can be outside the ring. A CRT may not fare so well near the ring, but a pair of LCDs, a large beam splitting pellicle and the proper retarders in front of the LCDs may suffice instead.
Angle of view is limited.
Projection may also work but a non-metallic screen which preserves polarization may be hard to come up with.