Hello Sin,
Sorry, I don't have an enviroment to test the code but you may be in the right way. Try to create a hardcoded relationship for test purpose. Something like this:
var CustomerNode : elementsof Customer.Relationship;
CustomerNode.RoleCode = 1234; // (put some valid role code)
CustomerNode.RelationshipBusinessPartnerUUID= 1i2u3i12u3i1u23i1u32; // (put a valid bp uuid)
this.Relationship.Create(CustomerNode);
Regards,
Alexandre.