integration data transformation via Groovy

What I'd like is something similar to how scripting is supported in web service checks. Particularly for HTTP integration.  If the script option is selected, then you get a template script and the script context has access to an "alert" object which has all the alert info you would expect from an alert object (i.e. same as the alert returned by the API).  As with web service checks scripting, the return value of the script would be the HTTP request payload passed to the integration, which is what I'd want to programmatically define in the script (JSON, XML, whatever).