You cannot do that since that admin cert configuration is same to all vdom. Instead you can use wild card certificate to the admin portal and point multiple subdomains to multiple vdom IP address, so you can access different vdom with different ip address with same wild card certificate.
For example, you can sign wild card cert wtih "*.xyz.com"
You can use vdom1 URL as "vdom1.xyz.com"
VDOM2 URL as "vdom2.xyz.com"
VDOM3 URL as "vdom3.xyz.com"
Hope this helps