No idea with synthetics, sadly. With naturals, the difficulty is often the opposite - it seems most synthetics are far sweeter than their natural counterparts and it's hard to sweeten up a natural fragrance to make it more "designer/niche like" without messing with the formula too much, or relying on the old standbys of vanilla, tonka, tolu balsam or benzoin. Of course, those alter the overall structure of the blend and is rarely ideal.
I'm interested to hear the responses here. I suppose one easy one fix would be "use some naturals."