Use the start and stop events. These events allow you to execute queries outside of a regular data flow and are not for processing records. On the event type (either start or stop), choose "JDBC Query". An extra tab will appear in the properties pane that allows you to define the query, the connection properties and driver (if necessary).

If you need to execute more than two queries, you can add a Dev Data Generator origin, check the "Produce Events" checkbox, and add a JDBC Executor off of the event flow of the origin.