If you are trying to feed default values to your model from an arbitrary source, see DefaultValueService. Attach your implementation using @Service annotation.
If you are trying to edit an OSGi service (as opposed to editing say an XML file), see Resource API which sits at a level beneath model element and provides property read/write into underlying data storage. You could build a resource that wraps around your OSGi service. See XmlResource for an implementation example.
You could try writing an custom PossibleValueService and add it to your model property @Service annotation so that you can browse for the possible values, please see the Sapphire samples for implementation and samples for PossibleValueService,mind that your possible value service need to achieve the Querying and other stuff you need for your OSGI services.