Not sure if someone posted this before, but i was very, very close to kill the Lone Wolf BOB on legendary, I just use the box to cover... i left the game on for 75 (maybe is not necessary to leave it all the time, i was just looking for credits...) and then i killed a blue elite, after i did this, the generals spawned.... 4 of them did, and i have seen that in any difficulty there is always an initial wave of generals, i managed to kill 2 of them, but if someone plays Co-op, it is more possible to kill those 4 generals, and then get the BOB to spawn, and possibly kill it.
BTW, if you check on halopedian about BOBs, i wrote about all the spawn points i have noticed, check it now if you dont mind.