I have the opposite problem! As a slow runner I can enter a run and the mileage tracker converts my cardio entry to a "walk"! Ha - while I may not be super fast, I want credit for those extra calories dammit! LOL
What you can do, is work out how many calories the actual run does burn (by starting a cardio entry and checking it - no need to complete it and add it). Do that once and find out what your running burns, perhaps per 10 minutes.
Thereafter, when entering mileage, you can manually enter calories burned, so you just input however much you burn when running, for that amount of time.
Just check your "what I burn running in 10 minutes" every 10lbs or so lost because that value will change as you lose weight.
Deb, in New Zealand