Use mouseover on horizintal axis to show variance between years

I have created a line graph that has months of the year on the horizontal axis and cost of the vertical axis.  The report also has the ability to select more than one year. is there a way to create a mouseover, perhaps along the horizontal axis, that would show a percentage increase or decrease between years?? Example is I mouseover month 6 and it would show me the difference as a percentage between costs for year  2013 ($53.01) and 2014 ($114.15)