How to allocate products in MTO senario

Hi Guys,

I have one requirement in my client:

There are two sales order A and B (both are MTO order) from same customer X.

Quantity in A is 100 pc while B is 100 PC.

For some reason, the client would like to produce more goods from customer order A . In this case, maybe client produce 103 for sales order A.

Then how can we make MRP run for B just with target quantity 97 (100-3), as it's same products requested by same customer?

My initial solution is that: after goods receipt from production order for SO A, we suggest client to do transfer extra material (3 in this case) from customer sales order stock A to B.

Any other good suggestions? Thanks!