Sorry but.. Isn't it the same as adding the heatbed temperature graph? Since now you are plotting two (groups of) lines (extruder and heatbed) I assume somewhere you are pushing the current extruder and the heatbed temperatures in the graph. Instead of pushing these two values, you have to push the three values.
It'll be easier for you, since you don't have to remember which is the current extruder. It'll be easier to read, because now on the graph you have no way to understand if the line was extruder 1 or 2. And you don't have to store the data
Then, if you say it's a hard work I have to believe you, since I did not read the code (and it'll take me ages to understand how and where you are pushing the data to the graph...
