We have seen similar things in the past. For example the "GPLed" version of PGP 2 which had two additional restrictions, one was that the long text file with the crypto political background must accompany all distributions of PGP. Clearly that was non-free but something which can easily be done with the GFDL.
Because PGP was software, not documentation. Such a clause would be prefectly ok for free documentation.
For example a book on networks might want to include the OOB-Data text from glibc. With 48 lines (w/o the example) it is clearly beyond fair use.
You can ask the FSF to make a execption for examples. This makes sense, and I doubt anyone would object.