You could, of course, create gel layers, and the determining factor in stability would be the firmness of those gels. However - and I suppose this is just a hunch - I seriously doubt that a gel firm enough to hold the weight of all the heavier layers above it (and you are asking for at least 3) would really be drinkable, unless you're aiming for the consistency of a "Jello shot".
A better idea, in my opinion, would be to simply change the densities of certain layers, and an effective (and tasty) way to do that is with sugar, or more accurately, sugar syrup. There's a type of syrup used in bartending called Gomme Syrup, which is a thick sugar syrup with Gum Arabic added to prevent crystallization (among other things).
Sugar, by itself, has very poor solubility in alcohol, but sugar syrups and gomme syrup in particular will have few problems, considering that's already how many mixed drinks are made (like Whiskey Sour). If you're feeling really adventurous, you could also use sugar alcohols such as sorbitol or xylitol, which dissolve readily in ethyl alcohol in solid form. However, these are much more potent (sweetness-wise) than sucrose and some people report gastrointestinal reactions, so use at your own risk.
Sugar syrups are very dense, so if you mix them thoroughly with a particular spirit, you'll end up with a heavier (and sweeter) version of that spirit. So to make your palindrome, start with what you'd normally put at the top (say GM for the B52), mix it with syrup (it shouldn't take an excessive amount - maybe 20-30% by volume, but you'll have to experiment), and layer that on the bottom. Then take the next-lightest, mix it with slightly less syrup, and continue. Once you reach what would normally be the densest liquid, layer the drink as normal up to the top with the "pure" spirits.
The more layers, the more math you'll have to do, because you'll need to make sure that you add just enough syrup to layer 2 so that it's lighter than layer 1 (bottom) but still heavier than layer 3, and so on. Unless you're prepared to make the drink very sweet, you'll need to be fairly precise in your calculations.
Disclaimer: I haven't yet tried this myself, as it's the first I've heard of anyone trying to do this. However, I see no reason why it wouldn't work with proper (careful) layering technique. In fact, I remember doing something very similar all the way back in primary school, called rainbow in a glass.
Best Answer
Cinnamon is the bark of a tree. It is either sold as rolled strips of bark (=cinnamon sticks) or ground.
It will not dissolve, neither in water nor in alcohol.
What you want to do is basically the same as was done commercially with the vanilla extract you are already using:
Extract the taste, then discard the bark itself.
Alcohol is a good choice for extracting volatile aromatics. You could try and soak a few cinnamon sticks or a few tablespoons of ground cinnamon in a "neutral" alcohol like vodka or - if you are using it exclusively for your signature drink - use the brandy. This process might take from a few days to a few weeks, so nothing you can do "on the spur of the moment".
Another good carrier for the cinnamon taste would be water. You can simmer a few cinnamon sticks in water, then sieve. This is the same method that is used for mulled wine or mulled cider. To extend the shelf life of the "cinnamon water", you might considering turning it into simple syrup by boiling it with an equal amount of sugar.
Whether you use water or alcohol is a question of personal taste and planned other uses. The shelf life of an alcohol based extract might be longer, but with a sufficiently high sugar content, clean handling and refrigeration the syrup will last long, too. Time is a factor: The syrup can be ready and cooled in an hour or so, whereas the alcohol will take significantly more time.
Both methods work for vanilla, too - you could even make a "instant mix" for your drink.
Be warned, though: Filtering ground cinnamon from a liquid can be quite a hassle. It tends to clog coffe filters, but is too fine to be held back by a sieve. If you decide to use ground cinnamon because that's what you have at hand, consider letting it settle at the bottom of your container and carefully decanting the liquid from top. A coffe filter or a cloth-lined sieve can catch stray particles. You should get much better results by using whole or coarsely crushed cinnamon sticks.
There has been an ongoing discussion on what kind of cinnamon to use, so a short wrap-up here:
Cinnamon is derived from a group of plants, which vary in their properties and compounds. Especially coumarin, a substance also found in tonka bean, woodruff and other plants, has been widely discussed for its toxicity and is regulated in the EU.
From a culinary point, the cheaper cassia, which contains more bark and is usually sold ground or in pieces, is often considered inferior in taste to the true cinnamon, which often comes in sticks.
I will not venture a statement here, neither on health nor culinary claims.
I am sure every reader of this post is capable of making an informed decision.