You should definitely concentrate on pushing through your heels when you're on the elliptical. Pushing with your toes is a major cause of foot numbness and can lead to plantar fasciitis. It probably feels odd to you if you're used to pushing with your toes, but maybe try with your heels for a few minutes at a time and see if it starts to feel more normal to you?
Other things that have helped me are loosening my shoes laces and going backwards half the time. It also went away with time -- perhaps my feet just adapted?
Best of luck to you -- I hope you don't have to give up the elliptical because it's a great cardio workout!