So, in the beginning implicit - the Variable is unknown - as it is declared with DATA statement, after the Implicit enhancement.
Yes, the variable is unknown at compile time. But at runtime you can access it dynamically with another field-symbol trick.
So something like this is possible.
This is possible due to the fact that in ABAP local variables are created when a subroutine/method is entered.
For me this is just some kind of academic example. One should see this only as a last resort.
This is a very fragile approach, because at the next upgrade SAP might have refactored (renamed or removed) the lv_local_to_this variable and you would hardly detext this until it leads to logical errors during integration testing. But of course there are ways to detect this in the BADI method...