FIM Portal Customization - specify an empty Portal String

In the documentation describing "FIM 2010 R2 Portal Customization" https://technet.microsoft.com/en-us/library/jj134312(v=ws.10).aspx I cannot see if it is possible to set one of the Portal Strings to be empty.

We would like to set the following:

   FinalizeRegistrationSubHeading1 - To contain custom text
   FinalizeRegistrationSubHeading2 - To be blank
   FinalizeRegistrationSubHeading3 - To be blank

I have tried the following but the empty <value></value> errors and therefore none of the custmisations are applied.  Same result with just a space.

  <data name="FinalizeRegistrationSubHeading1" xml:space="preserve">
    <value>Click on the 'Problems Logging In?' link from your Windows login screen</value>
  </data>

  <data name="FinalizeRegistrationSubHeading2" xml:space="preserve">
    <value></value>
  </data>

  <data name="FinalizeRegistrationSubHeading3" xml:space="preserve">
    <value></value>
  </data>
 
Thank you,
Alastair.