Generating ruby objects (hashes and arrrays) from json_builder templates

Is it possible to generate a ruby object (either a nesting of arrays or hashes or both) from a json_builder template?

I want to reuse my existing json_builder templates to generate multipart form post payloads with rest-client. My fallback plan is to generate JSON with json_builder and then parse it back into ruby objects and send that to rest-client but it seems less then elegant.
