An easy way to make it fail:

sudo mount -o remount,size=X -t tmpfs tmpfs /tmp (where X is like 5MB or so over the current usage of /tmp to not make other applications fail immediately).

Now use ./admin/InitDb.pl --createdb --import to import data into a new database. Tar will complain about not being able to extract all the data, but initdb will still continue to run SQL scripts on the database.