No, this is not at all possible on Thinkorswim. Best you can do are chart bubbles and you have very little control over their placement. You have to tie each chart bubble to two reference points. One is time based and the other is numeric.
Let's say you wanted to plot a chart bubble one bar to the right of the last bar on the chart. We can place this chart bubble at the low of the last bar on the chart:
def lastBar = IsNaN(close[-1]) and !IsNaN(close);
AddChartBubble(lastBar[1], low[1], "Test", Color.WHITE, yes);
That example shows you how you can do this. If you are writing your own code you should be able to work out ways to move the chart bubble vertically and horizontally in reference to the last bar on the chart.