I needed to apply multiple static IPV6 addresses to a single interface under Fedora/CentOS. To do this you'll need to add an IPV6ADDR_SECONDARIES line to your /etc/sysconfig/network-scripts/ifcfg-eth0 so that it looks like this:

IPV6_DEFAULTGW=2001:db8::1
IPV6_AUTOCONF=no
IPV6ADDR=2001:db8::50/64
IPV6ADDR_SECONDARIES="2001:db8::40/64 2001:db8::30/64"

Note: Addresses are added in reverse order. Outbound traffic will use the last secondary IP added.