Share 'equivalent run work-out on an elliptical machine?'

Is there any way to get close to an equivalent run work-out on an elliptical machine? I have an elliptical but do not have a treadmill. The winters have been mild enough that I only occasionally use the elliptical; however, this year most of my running has been on the elliptical. While I know that an elliptical, theoretically, burns more calories it does not seem to give me the same work out t...