Certainly the relationship between MJO and El Nino has been studied in a number of ways. I don't think you'll find a simple correlation chart for it. I believe what Adam Sobel was talking about, is that the MJO comes with increased westerly winds on its leading edge. These counteract the usual trade winds in the tropical Pacific, and create conditions consistent with El Nino development. Although the MJO moves through a region pretty quickly (in a week or so) as opposed to the mainly stationary ENSO pattern, it could possibly trigger the onset of an El Nino if one were already tetering on the brink of development. During the onset of the 1997-98 El Nino, in spring 1997, big-time MJO activity caused large westerly wind bursts in the western tropical Pacific that some scientists believe played a critical role in the development of that huge El Nino, or at least made the difference between its being a modest El Nino and a very strong one. The spring is the time of year when small changes can made a big difference in the growth of a phenomenon like El Nino that involves positive feedback between the anomalous winds and the anomalous SSTs. Timing of an MJO is therefore important. If an MJO comes at a non-critical time, it may not have much effect on the ENSO state; it just moves through and things return to how they were before the MJO passed. Remember also that the MJO has an opposing effect when it has passed: there is a suppressed convection region in its wake. So the trick is to get the enhanced convection to combine with the existing conditions in a way that brings the winds above a critical threshold to trigger a Kelvin wave and add to the heat content at the time when it matters for ENSO development.