I tried the top voted answer and found that adding to env_dirs the path to the environment does not work. However, adding the path to the parent directory of the environment does indeed work.

In summary:

if the conda env is located in /path/to/parent/new_condaenv, then

works

conda config --append envs_dirs /path/to/parent

Did not work (for me)

conda config --append envs_dirs /path/to/parent/new_condaenv