Joining Feature Views on Different Entities

[skt7]

Following is the current setup:

1. Source: 3 tables in a PostgreSQL database, each configured as a PostgreSQLSource
2. Feature Views: 3 feature views, one for each source
3. Feature Service: a single feature service that combines all the feature views

Now what we would like to do is combine the data from the feature views such that the join operation happens over different columns/entities. Let's say the feature views are fv_1, fv2 and fv_3 and we want fv_1 and fv_2 to join over cust_id, and fv_1 and fv_3 to join over prod_id

Is there a way to achieve this using Feast? Any inputs would be greatly appreciated