Toughy! Multiple X-Axis Interval Tick Marks on Line Graph?

[justnumbers]

Here's a tough one for ya. I have a time series plotting daily return data across 1.5 years. My line chart looks great, except for the x-axis. The beginning data does not start exactly at the beginning of the 13-week quarter, and not all quarters are exactly 13-weeks. Q4 is 13 weeks and 3 days, to capture 12/31/13.

My boss wants to see (you guessed it) the x axis tick marks of each quarter end, utilizing the daily data available. All of my data is currently in a pivot-chart so that I can easily manipulate my chart analysis.

So far, I have formatted the x-axis for 13 units (using only fridays), which has helped the most, but then it doesn't include 12/31 as a "tick" and it excludes my beginning data until the first quarter end. So I am looking to use specified tick intervals, if that's even possible.

Any thoughts? I need to keep it all in a pivot for flexibility.