Excel graphs--manipulating the scale

I'm trying to create a report on excel using a line graph with 4 different sources of revenue. One of the sources jumps significantly above the other 3 making them difficult to read. Currently, the y-axis goes from 0 to 5 million with a scale of 500,000. One revenue jumps quickly above 3 million and the others remain below 500,000. We would like to make the part of the graph from 0 to 500,000 larger relative to the 500,000 to 5,000,000. Any ideas on how to do this without creating a secondary axis?