POST for REST service with URL params

My service is REST style, using POST, however the URL for my server requires that some information is passed as URL params.

When I configure a new REST /POST service, these URL params seem to be send as URL encoded POST fields, but my server expects them on the querystring. How can I make the service configuration do what I need?

From curl, I call my service like this:

curl -i "http://myserver.com/services/v1/rest/Scripto/execute/GetChartDataXML?someparam1=blah -d "foo=goo"

I need Presto to respect the URL params, but still post other fields as URL encoded fields.

any ideas? (I'm a newb)