-I interface interface is either an address, an interface name or a VRF name. If interface is an address, it sets source address to specified interface address. If interface is an interface name, it sets source interface to specified interface. If interface is a VRF name, each packet is routed using the corresponding routing table; in this case, the -I option can be repeated to specify a source address. NOTE: For IPv6, when doing ping to a link-local scope address, link specification (by the '%'-notation in destination, or by this option) can be used but it is no longer required.
-I で指定できると思います。
例)
ping6 -I fe80::ead8:d1ff:fecf:b2b6%eth0 fe80::124b:46ff:febb:340f