The 'form' attribute can make it qualified:

<xs:element name="person">
   <xs:complexType>
      <xs:sequence>
         <xs:element name="name" form='qualified' type="xs:string"/>
      </xs:sequence>
   </xs:complexType>
</xs:element>

which validates:

<my:person><my:name>Milowski</my:name></my:person>

You can setup schema defaults by setting 'elementFormDefault' to 'qualified' and all local elements will be qualified by default:

<xs:schema elementFormDefault="qualified">

</xs:schema>