Letting a host run slaac and then add a static address is not good enough as the slaac address might be chosen for locally generated packets.
Define for every application your bind address - locally generated packets will use it. If it is not possible Use RFC 3484 source address selection for selecting static source addresses.
Actually, RFC 3484 would be the preferred mechanism over configuring every application. Application specific address binding should only be used for applications that need an exception to the host-wide source address selection choice. + Fewer surprises for your ops team + Lower probability of a mistake leading to incorrect source address selection + Reduced probability of configuration mistake time-bombs + Reduces the amount of configuration required for a host Owen