Bitter Orangecello

I'm making a homemade liqueur out of my prematurely-picked bitter oranges, and while it's aging,  I'm taking a look around at recipes and ideas for which "secret ingredients" to add to the mix. There are many liqueurs that use bitter orange, such as Curacao, Triple-sec, Grand Marnier and Cointreau. Because I'm using unripe oranges, the aroma profile is more vibrant and less sickeningly sweet. I will add sugar in the end, but I want the aroma to be very fresh and invigorating and want to add an element of surprise to this concoction, yet without taking away from the purity of the oranges. Tomorrow is the 7th day of maceration, and then I will add the sugar and let it mature for another week. I think tomorrow I will add a sprig of rosemary to the mix, and then discard it as soon as I add the sugar. Rosemary can be very overpowering. I might also pick a few leaves off the tree and add more of a petitgrain aroma. I'm trying hard to hold back from adding half a vanilla pod, and will save it for when the oranges are very ripe and luscious, to give it more of a velvety feel.