How do you add a PKI certificate to "My Certificates?"

I read the Apple KB article about getting certain individual certificate-requiring websites connected with PKI certificates, but it assumes the necessary certificates are already visible in the "My Certificates" category of the Keychain Access app. What if I have a certificate from my work computer that shows up in the "Certificates" category but not the "My Certificates" category? Is there any way to get them transferred into the "My Certificates" category so that Safari will recognize them?

Brian Green