Yah, unless there was room (and money) to put more lobes on, the usual method is forked rockers. This does bad things to the tappet face vs. cam lobe loading, but it must work or it wouldn't be so common. The rockers are really no more complicated than they look, and not much harder to design and make than common; they just have more bending moment in the cross plane, but IMHO this is intuitive and easily compensated for (FEA not necessary except for minimum weight) - you'll know it when you see it. This is also sometimes used to adapt a DOHC head to a pushrod block, losing the benefit of the cam but keeping the 4 valves.
