I can't find a photo now, but a friend has (or had) one of those plasma balls running inside a silver painted drain pipe in his mx-5 conversion. It looked quite natural filling the big hole where the ICE exhaust used to me, and looked suitably mysterious and "electrical" at night.
It was unfortunately underwhelming during the day; daylight completely washes it away. [ Edit: though, perhaps with a bit more power... ? ]
The below is the sort of thing; they can be much more impressive. He had to take off the base, obviously, and adapt it for 12 V operation (normally, it's USB powered):
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You would be viewing it from above in this photo, with the middle of the plasma in the middle of the "exhaust pipe".
I hope I'm not giving anyone any silly ideas...
?