Using a Hydrometer with Liqueurs and thickened liquors

[OCDistiller]

I bought a hydrometer to find the proofs of a honey liqueur, a spiced rum, and a bourbon I've made. I started with the honey liqueur and realized that the sugar content is changing the specific gravity of the liquid to the point that I couldn't find the proof.

Also, I've added small amounts of glycerine to both the spiced rum and the bourbon (5ml/Liter). Won't this also throw off the hydrometer?

How do I use the hydrometer to find the proof of these thicker-than-usual products I've made?

Thanks!