Correct, the appliance definition file does not have the rules to allow for this
This feature is still undocumented as I'm not sure if selected implementation is the right one. I'm thinking about moving this to operating system plugin configuration. This would mean that you could force using non-PAE kernels like this:
boxgrinder-build your.appl --os-config pae:false
or in BoxGrinder config file:
plugins: os: pae: false
The motivation behind this is that I would like to have appliance definition file operating system independent as much as possible.
P.S. In the meantime, to workaround - update this file: /usr/lib/ruby/gems/1.8/gems/boxgrinder-core-0.3.2/lib/boxgrinder-core/schemas/appliance_schema_0.9.0.yaml and replace it with this content: https://gist.github.com/993031. This should do the trick.
and thanks for the workaround.