You can configure buttons manually, or modify the fop2buttons table "context" field for your extensions by hand, but maybe this will break transfers to those extensions with the modified context if that context does not include the local extensions.
To test it out, with phpmyadmin or the mysql command line client modify the context field for a particular extension, and set it to your custom context name. After that, restart fop2 and try again.
Something like this, assuming your extension is "100" and your custom context is named "onlyLocal"
myslq -u root -p asterisk -e "UPDATE fop2buttons SET context='onlyLocal' WHERE exten='100'"