Salt might work, although I tend to think of using it more with savory flavors like Cynar. I would like to re-try this with Pierre Ferrand Dry Curacao in lieu of triple sec. I think the brandy base and the modest sugar would both help.
I've seen salt in recipes with Cynar before, and it's easy to imagine it working in lots of places where one wants to emphasize the savoriness of a cocktail. (Salt as cocktail umami?) Now, I've seen salt and citrus paired successfully (read: to the citrus's advantage) in cookery before, but never in mixology--not that my experience in either domain is expert-level. On the other hand, I've pinched salt straight into Cointreau, which, if done in a sufficiently restrained way, makes it interestingly more citrusy: the sweetness and bitterness recede, and the "flavor" presses forward--especially the flowery, nasal quality of the citrus.
I'm not familiar with Pierre Ferrand Dry Curaçao. I can see why a bit of sugar might balance things the way you want. But why the brandy base?