Twilio evangelist here.
Unfortunately I'm not sure there is a way to do this by using Twimlets since we don't have one that knows how to grab the body of the inbound message and use it generate the TwiML needed to send a new outbound message.
Its a good idea though and I've passed it to the team that owns Twimlets.
If you don't want to run your own server, then you could look at using a service like Parse (which has a free tier and an integrated Twilio SDK) to stand up a simple endpoint that takes the inbound message body and then asks Twilio to send a new outbound message with that body.
devin