ActionWebService - omit backtrace in error response

I'm using ActionWebService to expose a WebService of my application,
and I would like to control the error responses sent back to the
client.
At very least, I would like to prevent the XML to include the
backtrace.
How can I do this?

I wouldn't have thought the backtrace would be outputted in production
mode. Have you tried running in production mode? script/server -e
production