Hello Dave,
Newer Software should support natively but try the below:
<test device.set="1" device.sec.TLS.profile.cipherSuiteDefault1.set="1" device.sec.TLS.profile.cipherSuiteDefault1="0" device.sec.TLS.profile.cipherSuite1.set="1" device.sec.TLS.profile.cipherSuite1="ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384"/>
If this fails open a ticket.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Best Regards
Steffen Baier
Polycom Global Services