Threshold workout outside

Maybe a stupid question, but how do you guys approach threshold workouts outside. I usually do most intensity days indoors, but I want to be better to do them outside, and not feel like "this could have been done better inside". I live in an area without long climbs, so i need some tips.

Well should be pretty easy to just do 300 watts for 15 minutes, but I often find myself with an uneven power curve.

Tips for better, smooth power curve is appreciated. :)