Creating ContentType using the native excel spreadsheet template in /Forms/template.xlsx

I've created a ContentType and I would like it to use the excel spreadsheet template, just like if I create a new document library with the excel spreadsheet template. This is SharePoint 2010.

My content type def looks like this:

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
  <!-- Parent ContentType: Document (0x0101) -->
  <ContentType ID="0x01010015aec27014ee4d0c983f5e6547ed707d"
               Name="My Content Type"
               Group="Custom Content Types"
               Description="My Content Type"
               Inherits="TRUE"
               Version="0"
               DocumentTemplate="template.xlsx">
    <FieldRefs>
      <FieldRef ID="{F80289FB-D42D-47A5-B8B8-A75B4CA2C8C6}" Required="TRUE"/>
      <FieldRef ID="{E5544FB6-2168-4A0E-AB75-09E7097FD745}" Required="TRUE"/>
      <FieldRef ID="{8C743462-F786-4373-BF36-9D6A7808C43F}" Required="FALSE" ReadOnly="TRUE" ShowInDisplayForm="TRUE"/>
    </FieldRefs>
  </ContentType>
</Elements>

As you can see I'ved tried using the DocumentTemplate="template.xlsx" but that doesn't work. I appreciate your help.

Thanks.