Add a set amount of consumed calories without creating a custom food

Here is the scenario: I go out to get dessert at a local ice cream place. I want to log the calories as an estimate, which, being real, is probably close to 1000. I would like a way for adding some calorie count to my day without creating a custom food. There is no way to know what the stats of the food are, 1000 is some random guess just so I can log the fact that I ate a big treat.

My current workaround was to make a dummy custom food where 1 serving is 1 gram at 1 calorie, so I can just say I had 1000 servings to get that calorie count. But I would like an official way to do this. A previous app I used, Adidas Balance food tracker (discontinued), allowed this and I'd like to see the feature in Cronometer as well.