How to set the attribute Win64 to yes or no according to the bit of Windows Operating System?

I use burn to install prerequisites, including the .net framework and vsto runtime. I have to know if I can install these package, so I do some registry search, for example, on 32 bit Windows, the registry of VSTO Runtime is located at HKLM\SOFTWARE\Microsoft\VSTO Runtime Setup, but on 64 bit Windows, HKLM\SOFTWARE\WOW6432Node\Microsoft\VSTO Runtime Setup instead.

In this case, the attribute Win64 of the element RegistrySearch should be set to no on 32-bit Windows, yes for 64-bit Windows.

<util:RegistrySearch 
      Id="VSTORuntime" 
      Root="HKLM" 
      Key="SOFTWARE\Microsoft\VSTO Runtime Setup\v4R\" 
      Value="VSTORFeature_CLR40" 
      Variable="VSTORFeature" 
      Win64="xxxxx" />

Is there a way to set the attribute Win64 of RegistrySearch according to the bit of OS? btw, I know the build-in VersionNT64, but idk how to convert that to yes or no.