Groovy's Sql class generally only supports what the underlying JDBC api provides. Performing multiple statements is not generally supported but some drivers like the MySql one should support that as a configuration option. Try something like (adapt for your environment):
def props = [user: 'myuser', password: 'mypassword', allowMultiQueries: 'true'] as Properties
def url = 'jdbc:mysql:def driver = 'com.mysql.jdbc.Driver'
def sql = Sql.newInstance(url, props, driver)
I am less keen on the fix on Stack Overflow for the general case. It would work in most cases but would need some additional work to support for instance semicolon values inside strings stored in the database.