I've tried throat his boosters/nic alternatives and none of them work, at least not the way nicotine does.
Throat Hit Plus: Relies mainly on ethyl alcohol. Does virtually nothing but add a little warmth to the vape.
Diablo Loco: Straight up (and ridiculously strong) capsaicin. Much more of an irritating throat hit that hits you much differently than nicotine.
FlavourArt Flash: The successor to QHit (which isn't made anymore). A blend of organic material and capsaicin. No nic-like throat hit, mostly mild capsaicin. Not particularly good, hits very differently (and much more mildly) than nicotine. Has a grassy flavour of its own that may influence additional added flavours.
Cinnamon: Does provide a throat hit that's closer to nicotine than capsaicin, but can also irritate the lungs.
Black pepper extract: Not much different than capsaicin. Adds significant peppery flavour.
In the end, I'm afraid there's just no substitute for the throat hit of nicotine.