Seems like a neat idea actually. Just be careful on choosing whom to give a piece of the passphrase as it will be valuable in times of need. If in case one part of the passphrase is lost, creating the whole passphrase and safekeeping it would save you and your family in case one part was lost.
thats why you use static data, like a social security number or date of birth. so its readily available.. but without having to actually write down the data itself.
-snip-
But what if, say for example, all of the wielders of the passphrase were caught in an accident and you have no copy of the whole phrase, that means you already lose the funds if ever, so keeping one 'just in case..' would always come in handy, at least on how I view it.