No, that can't be done, at least not right now.
Echo is a Bluetooth speaker. It cannot connect to other Bluetooth speakers.
I suppose it would be possible for the Echo programmers to allow it to pair to other Bluetooth speakers. But I don't think it would be to Amazon's best interests. They probably would rather have you buy another Echo. I'm still waiting for when Amazon allows us to order a 2nd or 3rd Echo. But for now, it's still limited to 1 per customer.