This isn't exactly what you are asking for, but maybe it can help you achieve what you want?
I do it slightly different than your approach. I read the version from my 'main' assembly bundled with the wix installer, renames the msi filename to contain the version string, and sign it afterwards in a post-build event.
Resources:
https://stackoverflow.com/a/19371257/767926
https://stackoverflow.com/a/12323770/767926
To rename the msi to contain the version in the filename (wixproj):
<Target Name="BeforeBuild">
<GetAssemblyIdentity AssemblyFiles="$(SolutionDir)'HARDCODED PATH'\bin\$(Configuration)\'HARDCODED NAME OF ASSEMBLY'">
<Output TaskParameter="Assemblies" ItemName="AssemblyVersions" />
</GetAssemblyIdentity>
<CreateProperty Value="$(OutputName).%(AssemblyVersions.Version)">
<Output TaskParameter="Value" PropertyName="TargetName" />
</CreateProperty>
<CreateProperty Value="$(TargetName)$(TargetExt)">
<Output TaskParameter="Value" PropertyName="TargetFileName" />
</CreateProperty>
<CreateProperty Value="$(TargetDir)$(TargetFileName)">
<Output TaskParameter="Value" PropertyName="TargetPath" />
</CreateProperty>
</Target>
To sign the msi after the renaming (wixproj):
<PropertyGroup>
<PostBuildEvent>"C:\Program Files\Microsoft SDKs\Windows\v7.0A\Bin\signtool.exe" sign /sha1 'CERTIFICATEHASH' /v /t http://timestamp.verisign.com/scripts/timstamp.dll /d "DESCRIPTION" "$(ProjectDir)\bin\$(ConfigurationName)\'HARCODED PARTIAL MSI NAME'@(AssemblyVersions->'%(Version)').msi"</PostBuildEvent>
</PropertyGroup>
It's important to manually add/edit this post-build event in the wixproj file(use the editor), if you use the GUI it will mess up:
@(AssemblyVersions->'%(Version)')
Also, if you would like to sign your MSI's, make sure you add a description for the MSI, otherwise the UAC prompt will show a temporary filename. Resource: http://kentie.net/article/wixtipstricks/