You could, but laminated wood Is much easier. Basically it is hand railing, but it is then slides into thin strips. You affix brackets to the strains (right-angle wood blocks) and clamp the railing to them. Glue, a hundred clamps, voila. Remove, add balusters, attach. The stairs themselves act as the for,.
Trying to heat, bend, form a piece of wood using steam would be quite a project. Doable, but definitely a departure from typical methods. Also, with the glue/clamp you get little spring-back. Quite a bit more with stream....