I had to look at the source code for this, and I’m afraid this may not be possible for that feature. The restricted post IDs are not known before the suggestions query is executed, and afterwards the post IDs are not kept, so there is no way to check which title belongs to which post.
All I can do now is to change the code a bit and add a hook for a future release to make this possible. It should not be too complicated.
If you want, you can add temporary FTP access and I can try to make the modification for you with the custom code as well, at least I can test it on an actual use case before adding to the next patch.