Can I extend sump pump outlet with elbow outside the house?
Yes, your plan would work providing your sump pump can handle the extra head pressure, which it should.

Have you ever actually had a problem with this or is it the last thing to do on your "To do list"? I'm asking because I grew up in a house in the Midwest with the same layout as you have and we never worried about it. If the outlet was covered with snow and the sump pump actually needed to run, the water being ejected would be warm enough to melt any snow around the outlet pipe. 

You could pick up a few inches by re sloping the horizontal pipe under the porch. You've got 6" of slope over a 4' distance, you could raise the utlet from 2" to 5".... Good luck