How to add two default custom build tools?

Hi,

I'd like to add not one but two default custom build tools to my VS2012 C++-Project, distinguished by the file extension.

I tried the following

<ItemDefinitionGroup><CustomBuild Condition="'%(Extension)' == 'idl' or '%(Extension)' == 'odl'"><Command>call CreateTLBandIsolatedCOMManifest.cmd "%(FullPath)"</Command></CustomBuild><CustomBuild Condition="'%(Extension)' == 'mc'"><Command>mc -c -u -v "%(Filename).mc"</Command></CustomBuild></ItemDefinitionGroup>

but the IDE gives me the following error if I try to open the project file:

"The reference to the built-in metadata "Extension" at position 1 is not allowed in this condition "'%(Extension)' == 'mc'".

What is the correct way to achieve this?

Frank