HTTPS_PROXY doesn't appear to work on Deno Deploy

Although the Deno runtime docs describe HTTP_PROXY, and HTTPS_PROXY (), they do not seem to honored on Deno Deploy as the outbound request comes from Google Cloud and a connection to the PROXY does not appear to even be attempted when calling `fetch`.

Is there some other setting or trick that's necessary to get HTTPS_PROXY working, or is this a bug or current limitation of the Deno Deploy environment?