Unfortunately you cannot do this with EVTO since it does not integrate to the car directly. When/if Tesla comes up with a secure and published way to do this I would be willing to add it as an option.
But keep this in mind: The car already does this. It uses your last 30 miles or so for it's consumption metric and adds planned elevation change to the next stop. But this is only good if the speed, driving style, traffic, weather and other factors are constant, which they never are. This is why using the navigation and watching your estimated arrival SOC bounces around a lot. If your consumption changes during that drive, the cars estimate will change too.
So if I added this feature to EVTO it would be wrong most of the time. It's current method is supposed to be much more stable. Biggest issue is if the weather reported is different or you find yourself not driving the same was you thought you would be during planning.
So thinking out loud it might be best if EVTO just monitored your speed to see if it aligned with predicted and then also monitored the weather to see if it's changed. It currently checks the weather forecast if it's older than 6 hours. The weather is checked if you make a change or at least just select Save without a change in Edit Trip Details.