If you really must.
It seems to me the answer is in the many AAIB etc reports that I've read where the driver is referred to as the aircraft commander.
Taking a leaf from the senior service for a moment, we find that a commander is a person capable of navigating and commanding a ship of small to middling size. A commander gets three rings.
A captain on the other hand is the person who is experienced enough to get to play around with bigger vessels. He or she gets an extra ring.
So, if you must, perhaps your average <5700kg spamcan driver could claim 3 bars, on the other side of that maybe you get an extra one...
Of course these things are usually only awarded in military service. The presence of them in civilian life, particularly where it's not exactly de rigueur I suppose isn't actually a crime but I've always tended to consider them a bit faux.
At the risk of stirring the proverbial hornet's nest you may want to pause for a moment and consider TCT's honorary rank of light commander and her actually wearing the insignia. Is that more ok because she's been awarded it by a military body, or does it appear 'kitschy'?
I offer the above as a question and make no comment on the merit or otherwise of TCT's dress - it merely serves as a contemporary example of what some may consider to be a quandary that is at least slightly relevant to this discussion... you can choose where you sit on that particular debate!
FP.