Resolution: Calling dynamically db connection is not a supported feature currently. JDBC Connection info will be needed at config time to fetch output schemas for JDBCQuery, to retrieve input/output parameters info for JDBCCall etc. Therefore, to be able to specify it "dynamically", there will be some fundamental changes into JDBCQuery/Call activities.
There is an enhancement logged for the same (1-10X0T7).
One way I can think of is to have multiple JDBC Query, and depending on who calls the process have a transition for that JDBC Query.