Is it feasible to add the DB2 JDBC drivers to the sqlquery-plugin.jar, change the hq-plugin.xml file to include the DB2 driver, rename the service and deploy as a new plugin in a hq-plugins directory. I am not exactly sure what is in the SQLQueryMeasurementPlugin.class but it is probably generic jdbc database access setup, so as long as you pass it the driver name and it can be found by the DriverManager things should work.
I am guessing that plugins are loaded by their own classloader and only service name has to be unique to aviod conflict