Ability to enter sales forecasts in periods other than weekly - e.g. fortnightly, monthly

Sales forecasts in the Planning module can only be entered in weekly periods. Would like the option to enter forecasts for broader periods e.g. monthly. Furthermore, when sales orders are netted off against forecasts during MPS/MRP, would like the netting off (in buckets) to use the forecast period i.e. in months, not weeks. I have a client who need to plan manufacturing in months rather than weeks. If they spread their monthly forecast of 40 over 4 weeks (qty 10 per week) but receive an order for qty 40 in week 4 (and no orders in weeks 1-3), they will still be producing 10 per weeks 1-3 to meet forecast demand, then producing 40 in week 4 to meet order demand. In this example they would be producing 70 in a 4 week period to meet a demand of 40. If they were able to enter forecasts for the month without having to spread it weekly, in the above example it would see the total forecast demand of 40 for the month, an order demand of 40 for the month, and recommend to produce 40.