The import/export functionality needs to be built in using ctools exportables or any similar method. Take views and cck i/e as example.

you should be able to export settings per domain not all at once. Import should go the same way as well... per domain.

The preferred method of export would be to present text that can be copied and pasted. The import method would take the exact text from the export and insert the settings into the system for that domain.