s_client signature_algorithm extension

[Abhiram Shandilya]

Is there a way to add a specific signature_algorithm extension when using 
s_client to connect to an SSL server? Why does s_client negotiate 
ECDH-RSA-AES128-SHA256 when I use the cipher ECDH-ECDSA-AES128-SHA256? Is this 
because they are equivalent under TLS v1.2 when no "signature_algorithm" 
extension is sent in the ClientHello message? Or does s_client send all 
supported signature algorithms in the extension?
Thanks
Abhi