Advanced grammar in build options/parameters

I was wondering if it’s possible somehow to use the advanced grammar options to change build parameters depending on the architecture? I have a part in one of my snaps in which I tried the following:

        plugin: cmake
        - -DCMAKE_BUILD_TYPE=Release
        - -DENABLE_DOCS=0
        - -DENABLE_TESTS=0
        - on armhf:
            - -DAOM_TARGET_CPU=armv7
            - -DAOM_NEON_INTRIN_FLAG=-mfpu=neon

But I ended up getting an error with snapcraft complaining the schema was invalid: Failed to load plugin: properties failed to load for aom: The 'cmake-parameters[9]' property does not match the required schema: {'on armhf': ['-DAOM_TARGET_CPU=armv7', '-DAOM_NEON_INTRIN_FLAG=-mfpu=neon']} is not of type 'string'

I’m aware that I can achieve this using override-build, but it would be nice if this were possible using the advanced grammar syntax, if it’s not already possible.