Is it possible to make custom assertions based on your groovy assertions?

At the moment I'm using SoapUI Pro NG and this is part of a Test that I'm building:

1. - DataSource Step with an Excel sheet containing all expected values for the DB2 Database Table
2. - JDBC step that connects to the DB2 Database
3. - inside the JDBC step a script assertion for each value (about 30 assertions per table)
4. - Datasource Loop

I would like to have a custom assertion for that script assertion(3) that shows up in the assertions menu.
Do I need to dive into the custom soapUI factories to do this? or is there a simpler solution?