How to run Python tests against multiple Python conda environments?

I have a few carefully configured conda environments created using Anaconda. I have written a Python package that uses some of the packages and libraries installed in these environments. Now I would like to run the tests with each test file being executed for each environment to make sure the package can handle working with different Python versions and different set of 3rd party packages available.

Using a tox did not work for me because it tries to recreate those environments locally to run tests against. This is how my tox.ini file looks:

[tox]
envlist = py36, py27
skipsdist = True

[testenv]
basepython = 
    py36: C:\Users\user\AppData\Local\Continuum\Anaconda2\envs\Env1\python.exe
    py27: C:\Users\user\AppData\Local\Continuum\Anaconda2\envs\Env2\python.exe

commands = 
    {envpython} -m unittest discover

However, it is not possible to do just plain pip install into the environments tox creates on each run mainly because there are some compiled libraries and workarounds involved (which are solved in a conda environment - so I have to use those as they are).

I currently have a dummy .bat file with the following content:

"C:\Users\user\AppData\Local\Continuum\Anaconda2\envs\Env1\python.exe" -m unittest discover
"C:\Users\user\AppData\Local\Continuum\Anaconda2\envs\Env2\python.exe" -m unittest discover

which I execute in a Windows cmd to see the results. It does work, but I wonder whether there is any more Pythonic way to run these tests such using py.test or tox. I do not want to recreate the conda environments I already have; I just want to use different Python interpreters accessed at different locations to run my tests.