I haven't gotten to the hibernate extesion with 3.0 yet, but it looks like there is a pull request coming that will hopefully get it updated: http://forum.liquibase.org/topic/maven-hibernate
Interesting idea with the properties file. The type conversion is different in 3.0, the way to do it now is to create liquibase.datatype.LiquibaseDataType extensions. Each data type has its own class like liquiblase.datatype.core.VarcharType but if you create a subclass of the ones you need to control and return a higher value than LiquibaseDataType.PRIORITY_DATABASE Liquibase will use your class instead.
You would override the toDatabaseDataType(Database database) method and set parameters to be the default values if not set ad then call super.toDatabaseDataType(database)
Nathan