How to get Powershell Invoke-Restmethod to return body of http 500 code response

Invoke-RestMethod call returns only very unhelpful exception below and does not (as far as I can tell) allow you to collect the body content (JSON object shown in fiddler trace results). This seems a pretty bad implementation if so because http 500 definition is pretty specific that client should return the body of the response to help troubleshoot... Am I missing something?

invoke-restmethod -method Post -uri "https://api-stage.enviance.com/ver2/EqlService.svc/eql" -Body (ConvertTo-Json $eqlhash)  -Headers @{"Authorization"="Enviance $session"}

invoke-restmethod : The remote server returned an error: (500) Internal Server Error. At line:1 char:9...

Fiddler trace below

HTTP/1.1 500 Internal Server Error Connection: close Date: Thu, 12 Sep 2013 17:35:00 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 EnvApi-Version: 2.0,2.0 EnvApi-Remaining-Calls: 994,994 EnvApi-Remaining-Interval: 2684,2684 Cache-Control: no-cache Pragma: no-cache Expires: -1 Content-Type: text/csv; charset=utf-8

{"errorNumber":0,"message":"Current user has no rights to retrieve data from table 'CustomFieldTemplate'"}