proforma invoice for separate positions

Hello,

We want to create a proforma invoice for different positions separately. Now, the system creates a proforma from all positions in a Sales order. The problem is that between the separate positions we have different deliver dates. But it is not possible to deleted individual positions in the Proforma. E.g., In the sales order I have 4 positions. For two from them I need a Proforma because I will deliver it now. The other two will be delivered in 3 months.

How can I create a partial proforma invoice?

B.r.

David