POST with custom content type

Hi list,

the BaseX [1] REST interface requires me to send POST requests with a content- type of "application/query+xml". Is it possible to send such requests with Orbeon? As far as I know, the only way to send POST requests is to use an XForms submission, which seems to force the content-type to "application/xml" - at least, if I change the serialize attribute to the other content type, no serialization is performed at all.

Kind regards, Ralf

[1] http://basex.org/