Elliptical is not an option at this time; however, a number of folks have asked for it in the past.
FitDay is in the process of a major revision, and one of the upcoming developments may include adding this. I also believe that being able to customize an activity (similar to making a custom food) will be an option as well.
IIRC from posts in the past, people have been using "ski machine" or something like that, which basically approximates a similar number of calories.
And now that you don't have to be perfect, you can be good.