Urgent: Help reqd for designing layout

Hi,

I need some assistance is designing following scenario:

How to have a calculated column in the layout?

Consider a cost center group A having 3 cost centers rolled up under it. First amount is planned for group and then distributed either manually or using function to each of the 3 cost centers.

1. Now in the layout I want a column which shows % for each cost center of the total amount. Ex: if cost center group A = $300 and each cost center has $100 in it then for which cost center it should show 33.33%.

2. Also not if this % value is changed then figures should change accordingly. Ex: if for 1 cost center 33.33% is changed to 25% then now its amount should change to $75 and $25 should go to not assigned.

Note: there is no key figure in the cube which stores this % value. It is something which is required only during planning.

How can I achieve the above scenario?

Thank you,

sam