Hmm...

IIRC some of the security levels (B2? C2?) require that you can write a file but not read it, so it should be possible.

You could try adding group "CREATOR OWNER" to the directory and explicitly deny read access. This will allow the user to create the file, but the permissions when applied will deny read access.

I've just started using "CREATOR OWNER" on a share where I want everyone to have access to the data and to be able to read and write their own files but not change or remove anyone elses files.