How to restrict entering not multiple quantities in sales order lines?

Dear all,

We have business need to restrict in sales order line entering goods quantity which is not multiple of specified value (for example 100: if in package there are 100 pieces of goods, than sales order line quantity should be in multiple of 100).

Special conditions:

1.       Mentioned solution is needed only for one Operational Unit (OU) from 45 OU.

2.       One price-list is used for all OU.

3.       For every OU its own (separate) item validation organization is used.

4.       There are material transactions by goods that are intended to restrict entering without multiples and there is no possibility to change Unit of Measure.

5.       Oracle Process Manufacturing is not used.