This could be a situation to "mix and match". That is: collect the data via global level attributes but then create dynamic entity instances to handle the rules.
It will require a bit more work behind the scenes in the rules but could give a better user experience. It can depend a bit on just how many "shared" rules there are and just how much data you need to collect for each individual.
One thing you will need to be very careful of though is in relation to any data mapping with external systems (both inbound and outbound).
Han Joosten wrote:
Would it be possible to infer the entity instances, and then add base attribute values to the inferred instances? If so, how can this be done?
No, not with out-of-the-box functionality. Inferred entity instances may not contain base level attributes.
See the section 'Infer existence of entities to satisfy the relationship' in the article 'Write rules that infer relationships and entities: http://docs.oracle.com/html/E54499_01/toc.htm#Rules%20using%20entity%20instances/Write_rules_infer_relationships_entities.htm#Infer_existence (in particular, look at the 'Notes/Limitations' list)