How can I place multiple project dlls in the same Assembly Cache zip for Silverlight?

I'm using the very helpful 开发者_C百科MvvmLight toolkit and want to package both dlls into a single zip with Assembly Caching turned on. I tried to set the for both the main and the Extras.dll, but the app can no find the Extras dll in the zip. Is this possible to do with Silverlight?

EDIT: I'm using Assembly Caching so that the toolkit (and other dlls) are not in the XAP. Then the user will only need to download these one time, instead of once for every Silverlight app. We have a ASP.NET app with several different pages exposing different Silverlight apps.

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I've found that I can use the same zip file in each extmap file now. I'm not sure if I did it wrong before or what...

<?xml version="1.0"?>
<manifest xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <assembly>
    <name>GalaSoft.MvvmLight.Extras.SL4</name>
    <version>3.0.0.30106</version>
    <publickeytoken>918f02b0f4b4b116</publickeytoken>
    <relpath>GalaSoft.MvvmLight.SL4.Extras.dll</relpath>
    <extension downloadUri="GalaSoft.MvvmLight.SL4.zip" />
  </assembly>

</manifest>

<?xml version="1.0"?>
<manifest xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <assembly>
    <name>GalaSoft.MvvmLight.SL4</name>
    <version>3.0.0.30106</version>
    <publickeytoken>918f02b0f4b4b116</publickeytoken>
    <relpath>GalaSoft.MvvmLight.SL4.dll</relpath>
    <extension downloadUri="GalaSoft.MvvmLight.SL4.zip" />
  </assembly>

</manifest>