Pen rest with weight chamber.

thingiverse

You'll find a recessed area in the standard pen holder part of the modular stand, which provides space for halting the print process temporarily to incorporate additional weight - this could be achieved using pennies or lead fishing weights as examples, and also with small BBs - all of these options allow you to achieve more even prints by compensating for differences in ballast throughout. This ballast pocket ends approximately 32.1 mm from where the tapered portion begins, meaning that if you want to incorporate a layer specifically, divide your current print resolution (or layer height) into this distance and pause the print on the resulting calculated layer number to get accurate weight distribution results.