I've done a few examples of this sort of thing that could possibly help:
• Example 1: Here I use xy annotation to make custom xtrace labels that move with the xtrace crosshair
• Example 2: In this example, I place actual PMILabels in the chart, so they correspond with a varied bar position. Later in the thread, after the OP changed chart types, I also do another xy annotation example.
My guess is that the actual labels will be a better approach for what you are trying to do, since it appears that you are wanting the labels to be outside of the plot.