that buttered rum sounds awesome.
In the interest of keeping things light and simple, my recommendation would be to carry (one) additional, but potent ingredient to add to the flavor of your booze.
Highly personal recommendation - but for me and my love of all things scotch, it would be allspice dram. (think cloves in a bottle)
.25oz of allspice dram for 1oz-1.5oz of whisky is perfect - add water as needed.
(Side note: If in the comfort of your own home, the recipe should be: .25 allspice dram, .5oz simple syrup, peaty scotch, bitters, ice + orange peel / twist of an orange)