How to associate application with existing file types using WiX installer?

Related to this: How to register file types/extensions with a WiX installer? but not a duplicate.

I need to handle existing file types (.jpg files).

I do not want my app to be the default handler for .jpg. I would just like to extend the "Open with" menu with a link to my app.

I see HKCR\.jpg\OpenWithList\ and HKCR\.jpg\OpenWithProgIds\ in the registry but I am not sure whether to write to these and how to do it correctly with WiX. Should I use something like this?

<ProgId Id='??what here?' Description='Jpeg handled by my App'>
  <Extension Id='jpg' ContentType='image/jpeg'>
    <Verb Id='openwithmyapp' Sequence='10' Command='OpenWithMyApp' Target='[!FileId]' Argument='"%1"' />
  </Extension>
</ProgId>

There are many ways to fail here (like Photo Mechanics did, the HKCR for image file types is a real mess after I have installed this software).

How to do this correctly with WiX?

Here's a full, complete example with a bit more detail and cleaner code than in the linked question and should provide a better answer. Quite timely as I've recently finished porting the code posted previously, to use proper ProgId elements so this is fresh in my mind ;)

In regards to the 'what here', you can pretty much use whatever you like :)

<Icon Id="filetype.ico" SourceFile="filetype.ico" />
<Component Id="MyApp.exe" Directory="APPLICATIONFOLDER" Guid="*">
    <File Id="MyApp.exe" Name="MyApp.exe" KeyPath="yes"/>

    <Shortcut Id="startmenuShortcut" Directory="ProgramMenuFolder" Name="MyApp" Icon="$(var.product).ico" IconIndex="0" WorkingDirectory="APPLICATIONFOLDER" Advertise="yes" />

    <!-- Capabilities keys for Vista/7 "Set Program Access and Defaults" -->
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities" Name="ApplicationDescription" Value="!(loc.ApplicationDescription)" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities" Name="ApplicationIcon" Value="[APPLICATIONFOLDER]MyApp.exe,0" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities" Name="ApplicationName" Value="!(loc.ApplicationName)" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities\DefaultIcon" Value="[APPLICATIONFOLDER]MyApp.exe,1" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities\FileAssociations" Name=".xyz" Value="MyApp.Document" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities\MIMEAssociations" Name="application/xyz" Value="MyApp.Document" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\MyApp\Capabilities\shell\Open\command" Value="&quot;[APPLICATIONFOLDER]MyApp.exe&quot; &quot;%1&quot;" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\RegisteredApplications" Name="MyApp" Value="SOFTWARE\MyApp\Capabilities" Type="string" />

    <!-- App Paths to support Start,Run -> "myapp" -->
    <RegistryValue Root="HKLM" Key="SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\MyApp.exe" Value="[!MyApp.exe]" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\MyApp.exe" Name="Path" Value="[APPLICATIONFOLDER]" Type="string" />

    <!-- Extend to the "open with" list + Win7 jump menu pinning  -->
    <RegistryValue Root="HKLM" Key="SOFTWARE\Classes\Applications\MyApp.exe\SupportedTypes" Name=".xyz" Value="" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\Classes\Applications\MyApp.exe\shell\open" Name="FriendlyAppName" Value="!(loc.ApplicationName)" Type="string" />

    <!-- MyApp.Document ProgID -->
    <RegistryValue Root="HKLM" Key="SOFTWARE\Classes\MyApp.Document" Name="FriendlyTypeName" Value="!(loc.DescXYZ)" Type="string" />
    <ProgId Id="MyApp.Document" Description="!(loc.DescXYZ)" Icon="filetype.ico" Advertise="yes">
        <Extension Id="xyz">
            <Verb Id="open" Command="!(loc.ExplorerMenuOpenXYZ)" Argument="&quot;%1&quot;" />
            <MIME Advertise="yes" ContentType="application/xyz" Default="yes" />
        </Extension>
    </ProgId>

    <!-- Optional: add an 'Edit with XYZ' to 'right click' even when not associated -->
    <RegistryValue Root="HKLM" Key="SOFTWARE\Classes\SystemFileAssociations\.xyz\shell\edit.MyApp.exe" Value="!(loc.ExplorerMenuEditXYZ)" Type="string" />
    <RegistryValue Root="HKLM" Key="SOFTWARE\Classes\SystemFileAssociations\.xyz\shell\edit.MyApp.exe\command" Value="&quot;[APPLICATIONFOLDER]MyApp.exe&quot; &quot;%1&quot;" Type="string" />
</Component>