So I ended up creating a .Rprofile script by first creating an environment variable called R_PROFILE_USER which held the file path to where I'd be saving the .Rprofile file ("C:/users//Documents/.Rprofile"). I then made that file, which was comprised solely of the following:
.First <- function() {
.libPaths(c("c:/users/<user>/R/library/3.6", .libPaths()[2]))
}
R now knew to not look in the default location, which could be found with path.expand("~"), for packages, and instead look on my C:/ drive. As a result, I did not need to specify lib when calling install.packages().
It's worth pointing out that this is typically considered bad practice. See this thread for some insight from Henrik Bengtsson on why specifying your own library for R packages to be saved can be problematic. The only reason I'm doing it in this situation is because the location R wanted to use by default was causing issues.
Hope that helps.