Here comes nicer sketches of direct addition and a wick system based on a tent of stainless steel:

Figure 8 shows a tubular wick technique. Wicking material is supported on pipes of wire mesh and soaked with oil as required. The foam level rides just below the wicks, and oil is drawn into the foam in small amounts. This minimizes excess oil being consumed by metabolism. We have observed oil usage reductions of 25 to 50 percent with wicks or with carefully adjusted continuous feeds. Furthermore, a constant foam level minimizes the severe environmental changes mentioned earlier.

Figure 9 shows the tent-shaped wick support. This allows oil to be dripped on, rather than to be forced outward through holes in the supporting pipe, and there is nothing to clog. The wick method has also been useful in controlling foam in our filtration surge tanks where flow removes oil rapidly if added to the liquid. Further processing was easier when the troublesome excess oil was eliminated.