Heres what I did:
<IfDefine SSL>
Listen xxx.xxx.xxx.xxx:443
</IfDefine>
And:
<VirtualHost xxx.xxx.xxx.xxx:443>
In /root/ispconfig/httpd/conf/httpd.conf
Then just point a hostname at that ip address and setup ISPconfig to work with that hostname and you have
https://yourhostname without the silly :81