Adding arguments to installer using NETSparkle appcast.xml

Question

I'm using NETSparkle for auto updating my .NET app. I have the following in my appcast.xml for my new version:

 <item>
      <title>Version 2.0</title>
      <sparkle:releaseNotesLink>http://blah/1.2.0.html</sparkle:releaseNotesLink>
      <pubDate>Sat, 19 Oct 2013 13:20:11 +0800</pubDate>
      <enclosure url="http://blah/Setup.2.0.exe" sparkle:version="2.0" type="application/octet-stream"/>
 </item>

Since netsparkle relaunches the app after installing the update, I don't want the installer to launch it. So I added a "/norun" arg to my installer so it will skip the "launch now" option at the end.

But I can't figure out how to pass an argument to the setup.exe in my appcast.xml?

I was thinking something like adding: sparkle:arguments="/norun" to the <enclosure>, but no dice.