Is there a way to have a drop-down selection list which is dynamically populated from a common file?

For example:

I create 2 flexinode types: A and B.

In node A, I want to include a drop-down selection list called 'members' which contains an up-to-date list of names. Currently I have to update the list manually.

In node B, I also want the same 'members' drop-down list, identical to the one in A. Currently I have to manually create and update this one too!

Is there some way that different flexinodes could share the same list - a common file? Presumably this would have to be external to A & B.

Would it then be possible to call this file from the relevant part of the drupal SQL database ... eg UID ... ?

... the dream ends at that point and I wake up drenched in sweat.

I suppose you might be able to do this with a Template hack?

I think this request might be related to the 'flexinode relations' http://drupal.org/node/8468 but I'm not clever enough to understand that discussion :P