How to force the urlUtils proxy perform only POST requests

How can I force the urlUtils to use only POST requests. I a using it as shown in the following block described also in the how to use proxy section, and I have noticed that some times (maybe when the request is less than 2000 characters ) it performs GET request, which in my case is not an accepted solution.

urlUtils.addProxyRule({
urlPrefix: "route.arcgis.com",
proxyUrl: "<url_to_proxy>"
});