Excel Pivot Table Custom Field for Yearly Growth

I have the following type of data:

		2010	2011	2012	Grand Total
Gross		$100	$150	$200	$450
Services	$60	$75	$120	$255
Products 	$40	$75	$80	$195

The years are part of a group that came from montly data source, which looks like this:

		Services	Products
2010-Jan	$36		$12
2010-Feb	$14		$12
2010-Mar	$44		$12
2010-Apr	$14		$12
2010-May	$45	 	$5
2010-Jun	$11	 	$54
2010-Jul	$34		$23
2010-Aug	$24		$51
2010-Sep	$44		$55
2010-Oct	$79		$22
2010-Nov	$87		$32
2010-Dec	$11		$75
...
(the numbers are just examples, they don't add up)


I would like to have additional columns in my Pivot Table that show the growth amount for each year, as well as the percentage.
Something like this:

		2010	2011	Growth	Growth %	2012	Growth	Growth %	Grand Total
Gross		$100	$150	$50	50%		$200	$50	33%		$450
Services	$60	$75	$15	25%		$120	$45	60%		$255
Products 	$40	$75	$35	88%		$80	$5	14%		$195

How can I achieve this?  I've been at this for days, and have not been able to figure it out.

Thanks!