Automatic Inheritance of user defined fields in IM structure

Hi All,

Our requirement is to automatically inherit user defined fields from the top level of the Investment Program into the bottom ones. This user defined field will be filled in only the Program top level and whenever a new position ID is created subordinate to the top this user definedfield will be filled in from the top.

As far as I know we have no provision for setting up substitution rule which we normally do for a cost object. Do anybody know how this can be acheived or through user exits?