In a web.config file how can I append to PATH

Question

I have a 3rd party dll that needs to be loaded by my Web app. It requires a bunch of other files that are in its directory and I don't want to try to copy them all over to the Web app. If I set the system PATH, it can find it at run time. But I think having to set the system PATH is a bad idea. I want to make my Web app set its instance of PATH instead. I am wondering if I can somehow do this using something like environmentVariables in the Web.config like this:

  <system.webServer>
    <aspNetCore .....>
      <environmentVariables>
        <environmentVariable name="SOME_ENV_VAR" value="Development" />
      </environmentVariables>
    </aspNetCore>
  </system.webServer>

But I would like to take the existing PATH and append to it instead of replace it.