Sending Locals with Docpad API

[Rolilink]

Is a good idea to send some locals to the plugin Via the Docpad API, something i need to do requires the use of some javascript mixins and i cant send it when serving the document on express.

tried this:

docpadInstance.serveDocument({
    document: document,
    req: req,
    res: res,
    next: next,
    locals:{
       val:rval
     }
});