Multiprovider and cumulative data

hi, i've got two cubes - one with data, and another one with cumulative data.

Eg:

Cube 1: Position 1a $ 10

Position 1b $ 3

Position 1c $ 2

Position 2 $ 40

Position 3a $ 0.5

Position 3b $ 1.5

Cube 2: Position 1 $ 15

Position 2 $ 40

Position 3 $ 3

Now i need an report over this two cubes with both cumulative data (from cube one and two) - and the difference, if there is any (here at position 3). I thought i could do this with a multiprovider, but the sap-help says: "In a MultiProvider, every characteristic in each of the InfoProviders involved must correspond to exactly one characteristic or navigation attribute" - but in my case i think i have to map position 1 a,b and c to position 1 and so on.

Is there any way to achieve my with an multiprovider, or is there another solution for my problem?

Thanks in advance