So, get them to register by applying for a hearing under 245(i), then we know where they are, don't we?
Since the point of 245(i) is to "change status" of Illegals, knowing where they are doesn't really help in this case, since they would no longer be deportable.
Some more misrepresentation of facts from you.245(i) only changes the mechanism by which they get to apply for change of status, and while it is true that while their applications are being reviewed they are not deportable, it neither guarantees a hearing, nor does it guarantee a change in status.
Hence, once the determination has been made that they do not qualify either for a hearing, or for permanent change in status, they are very, very deportable.