@GobyOne not sure I entirely understand the target outcome, but geom_rug() might be helpful? https://ggplot2.tidyverse.org/reference/geom_rug.html
Or potentially, for a slightly different visual effect, something from ggdist: https://mjskay.github.io/ggdist/index.html
@GobyOne geom_rug may be what you're looking for, possibly? Or just use y=Inf with geom_point.
@GobyOne I second the geom_rug() and {ggdist} options already mentioned. Might also suggest having a look at {ggside}: https://github.com/jtlandis/ggside
It's designed for adding plots to the sides of plots (essentially in the margin area)