You can set showinaddressbook for each synced object using a custom mapping.

You will need the DN of the addressbook(s).  For multiple addressbooks, insert multiple showInAddressBook mapping lines.

To do this, you will need to know your local CN (placeholder cn=dirwiz below) and DC tree (placeholder DC=dir,DC=domain,DC=com below).  If you don't know these values, open ADSI Edit and drill down under the 'Configurations' tree to identify the values. Note: If the 'Configurations' tree is not visible, you can turn on the connection to show it.

The following is an example of a custom mapping that sets two (2) addresbook settings. Each showInAddressbook line should appear in the map file as all one line, no carriage returns.

showInAddressBook=CN=All Contacts,CN=All Address Lists,CN=Address Lists Container,CN=DirWiz,CN=Microsoft Exchange,CN=Services,CN=Configuration,
DC=dir,DC=domain,DC=com

showInAddressBook=CN=Default Global Address List,CN=All Global Address Lists,CN=Address Lists Container, CN=DirWiz,CN=Microsoft Exchange,CN=Services,CN=Configuration,DC=dir,DC=Domain,DC=com