Hibernate version: 2.1

Hi I'm running hibernate with the HSQLBD database. I have a users who need to be able to update their schema remotly. I then make a installation for them to install with new xml files and cfg-file and hsqldb log file containing the new schema etc.

Now, my problem is that schemaupdate also drops the database before creating new table structure. I need the information within the database to be intact after schema update. Is there an automatic way to do just alter table when possible? (I understand that there might just not be always possible)
Thanks
/Martin