Split site onto 2 servers – Cert. Issues

Currently:
Web server inhouse hosts main site and home banking site within main site. Verisign certificate for www.mycreditunion.com is on home banking log in page.

Planned:
Move main site to ISP hosted site. Keep home banking inhouse. Hyperlink the two sites. I know I need two Verisign certificates, one for each server.

I can move the V Cert off the inhouse and put it on the hosted site because the cert is for www.mycreditunion.com and that is where the site will be.

What do I do with the home banking server? Buy another domain name? Can I get buy with an IP address? Verisign has not been helpful in getting this resolved.