Bex characteristic issue

Hello All,

can some one share your ideas in achieving the below requirement

requirement as below.

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• If a PO is having Final invoice as # then the result should show only one line for the keyfigure values if we drag final invoice to free char area.
• If a PO is having Final invoice as X then the result should show only one line one line for the keyfigure values with X if we drag Final invoice to free char area.
• If a PO is having Final invoice as both X and #, then the result should show only one line as X(not #) but with cumulative value  of both X and # if we drag    Final invoice to free char area.

The  first 2 points we can achieve as normal and the third one is the tricky one.

any ideas to acheive point # 3?