Rolling 12 months in Web Intelligence with an additional dimension like Customer or Client?

Hi Gurus,

I had 2 requirements from customer:

1. Normal rolling 12 months sales consisting of dimension Year and Month

i.e Rolling 12 month for Jan 2014= Sales(Feb 2013)+Sales(March 2014)..................................Sales(Jan 2014).

Formula used: =If [Sales]In([Year];[Month])<>0 Then NoFilter(RunningSum([Sales])-RunningSum(Previous([Sales];12)))

   2. Rolling 12 month with an additional dimension like Customer, so to achieve rolling 12 month for each customer.

As my previous formula is cell based, it wont work if i add additional dimension. I have tried creating various formula using context formula like IN (Break) and Previous. But could not achieve the desired result.

Please can you help me with 2nd requirement.

Regards

Sushant