Hello,
You can use MMP in APO-PPDS if you are using VC and your SO s are using a highly configurable material with object dependencies and all. There is a algorithm - Prioritised equal distribution which will split the planned orders into smallar quantities and distribute evenly. Other algorithms also can be explored.
If you want to convert the Planned order (got after a MRP in ECC for the sales order) and split it into equal parts over a month, then you can do that in a Planning table in ECC .
Hope this helps.
Hemant