In exclusivity, yes, it's possible.
But that's looking solely at the activity itself and not any extra calories you're burning on top of your regular activities (so no, you're not burning a total of 3,000 calories just standing, theoretically assuming your daily burn is 2,000).
If you're accustomed to doing this (as it sounds like you are since you state that it's what you do for your job), then it's part of your lifestyle and you're not burning anything extra.
Don't forget that when you log it, this replaces your sedentary burn for the same time period. You're burning 125kcal/hour standing or over 1000 kcal in total, but you'd have been burning 100kcal/hour sitting or about 800kcal in total.
Stick it in your log and you'll see that your predicted total burn for the day will only increase by however many extra calories over sedentary this is. If you've done the sensible thing and set yourself to "lightly active" because you're standing a lot at work you should see that the predicted burn doesn't change much if at all because the formula CC uses to calculate the estimate for your calorie burn (Mifflin-St.Jeor last time I checked) gives a pretty reasonable estimate if you aren't a 3-5 standard deviations outlier.
