I've jigged for bottomfish off Haida Gwaii for 40 years, and I'd say about 1/3 of the biggest lingcod I've caught have been on rockfish. I've never intentionally put one on for bait (who wants to handle those spines on purpose?), but on many occasions, when the black or dusky rockfish at the edge of a dropoff are so thick and aggressive that you can't get a jig down through them, I've finally just let the weight of my 6 or 8 ounce jig carry a hooked rockfish over the dropoff, and had a big ling take it.
If you've ever gutted a big lingcod and seen a rockfish in its stomach, you'll know that the lingcod first chomps down on the rockfish to subdue it, then swallows it headfirst. Any other position would mean trying to get the rockfish down its throat with the dorsal spines standing up and digging in, making a case of human strep throat look like a walk in the park with a cheerful grandma.
As a result, large lings clamp down hard on your hooked rockfish, and they're very reluctant to let go, meaning you can steadily haul the ling to the surface, and gaff him without ever having hooked him. It's also not at all uncommon to bring up a big ling this way, and have another big ling swimming up beside her, in which case you can let the first ling hang just below the surface, gaff the follower, and then gaff the one that's holding the rockfish. It's a way to score a double-header without hooking either fish.
Since I've learned the wisdom of releasing any lingcod I catch that weigh more than about 20 pounds, I've taken to tapping the bigger ones lightly with the gaff handle to make them let go of the rockfish. It's often amazing how hard it is to get them to give up, although possibly their rows of fangs are set in so tightly that they can't easily release their grip.
My biggest kept lingcod, caught in the 1980's, weighed 62 pounds, and after seeing its coarse, parasite-laden meat, I vowed never to kill another big breeder. It really irritates me to see charter operators advertising "trophy lingcod"! Who would hang one on the wall, and who would choose it as food?