odata request too long

I use REST.js library to fire the RetrieveMultiple-message on a custom entity. A plugin handles the request then.

var result = SDK.REST.retrieveMultipleRecordsSync("rt_command", options, function(error) {
                });

the "options"-string is long. As far as not encoded it is less than 2048 chars and the call works fine.

As soon as encoded 

options = encodeURI(options);

it grows and the call fails (fiddler reports 404.15 The request filtering module is configured to deny a request where the query string is too long).

Is it possible to send the POST instead of GET? Wich options do I have?

Thank you