Sorting pivot tables rows by column first entry

[Derek Cavanagh]

I wish to sort the row (customers) by the date of their first invoice. This should enable be to see the build-up of revenue by customer. See below for desired result.. I wish to sort customer by the date of their first invoice within the pivot table if possible. Thanks
[TABLE="width: 500"]
<tbody>[TR]
[TD][TABLE="width: 448"]
<tbody>[TR]
[TD]Row Labels[/TD]
[TD]Jan[/TD]
[TD]Feb[/TD]
[TD]Mar[/TD]
[TD]Grand Total[/TD]
[/TR]
[TR]
[TD]Starfish[/TD]
[TD] 249[/TD]
[TD] 249[/TD]
[TD][/TD]
[TD] 498[/TD]
[/TR]
[TR]
[TD]Care[/TD]
[TD] 199[/TD]
[TD] 199[/TD]
[TD][/TD]
[TD] 398[/TD]
[/TR]
[TR]
[TD]Illumine[/TD]
[TD] 199[/TD]
[TD] 199[/TD]
[TD][/TD]
[TD] 398[/TD]
[/TR]
[TR]
[TD]WES[/TD]
[TD] 199[/TD]
[TD] 199[/TD]
[TD][/TD]
[TD] 398[/TD]
[/TR]
[TR]
[TD]Boya[/TD]
[TD] 599[/TD]
[TD] 599[/TD]
[TD][/TD]
[TD] 1,198[/TD]
[/TR]
[TR]
[TD]Vision[/TD]
[TD][/TD]
[TD] 3,469[/TD]
[TD][/TD]
[TD] 3,469[/TD]
[/TR]
[TR]
[TD]Jacob[/TD]
[TD][/TD]
[TD] 500[/TD]
[TD][/TD]
[TD] 500[/TD]
[/TR]
[TR]
[TD]Turning[/TD]
[TD][/TD]
[TD] 320[/TD]
[TD][/TD]
[TD] 320[/TD]
[/TR]
[TR]
[TD]Hyperion[/TD]
[TD][/TD]
[TD] 122[/TD]
[TD][/TD]
[TD] 122[/TD]
[/TR]
[TR]
[TD]ACM[/TD]
[TD][/TD]
[TD][/TD]
[TD] 6,015[/TD]
[TD] 6,015[/TD]
[/TR]
[TR]
[TD]Enable[/TD]
[TD][/TD]
[TD][/TD]
[TD] 249[/TD]
[TD] 249[/TD]
[/TR]
[TR]
[TD]Grand Total[/TD]
[TD] 1,445[/TD]
[TD] 5,855[/TD]
[TD] 6,264[/TD]
[TD] 13,565[/TD]
[/TR]
</tbody>[/TABLE]
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</tbody>[/TABLE]