In Ellucian Advance, there is dedicated functionality for this relationship, called "Covering Accounts". On the record of the Foundation, these are entered as "Covered Entities". Advance also includes functionality to soft-credit any covered entities whenever a gift is received from the covering organization.
My US$0.02 worth; the usual disclaimers apply.
Alan S. Hejnal
Data Quality Manager
Smithsonian Institution - Office of Advancement
600 Maryland Ave SW Ste 600E
PO Box 37012, MRC 527
Washington, DC 20013-7012
Voice: 202-633-8754 | Email: HejnalA@si.edu