In theory putting the capsules as close together as possible and reversing polarity on one will yeild a figure 8 emulation. In practice the distance between the diaphragms will cause phase anomalies. Specifically, there will be big phase problems at and around the frequency whose half-wavelength is equal to the distance between the 2 diaphragms [e.g. if the capsules are about 1" apart, frequncies around 6500hz will be most problematic] - the closer the capsules are, the higher the frequencies affected. You would need to get the distance between the diaphragms below 1 cm. to raise the problem frequncy above the range of human hearing. What will this mean to the sound? Well, that will depend on the source, and what you're trying to do with the "fig.8" - it won't hurt anything to try it and see. If you're trying to do a M/S pair, I suspect you will end up with very unnatural stereo imageing and/or loss of high frequency detail.
Scott