negative idiolect? why bother trying to describe something that doesn't happen? it's akin to a problem we run into all the time in writing software requirements: the software shall not [do something under unusual circumstances] -- not only can it be difficult to code a negative, but it is usually nigh onto impossible to test. but I digress. why not just say that your idiolect *disincludes certain structures.
-joe (i was able to change the subject) friday