Just for completeness: On Apache you would rename the conf file so that the site you wish to be the base site comes first. So, in /etc/httpd/conf.d I have:
So I renamed owncloud.conf to aa_owncloud.conf so the listing now looks like
and now the correct certificate (after restarting apache) is delivered to non-SNI capable clients. Happy days. Perhaps I could put this info in a wiki somewhere. Is there one? I spent ages trying to get SSL to work with a self-signed cert before I read the entry in the FAQ about SNI support.