Salutations,
As you have investigated, the XY graph doesn't store points like a "chart" does. In this case, why not just insert (insert into array) the values you desire into a matrix and have that replotted? Granted, you'll be forced to replot everytime something goes down, but such is life. Or just wait until all the data has been analysed and then plot it?
Sincerely,
ElSmitho