Part reservation to allocation

Has anyone come across a method to get the part reservation quantity to carry through to the allocated quantity?

The basic scenario would be:
An order is received for a specific quantity e.g. 1000pcs
We plan a load - may be for internal or external customer - and in doing so, we reserve stock. Due to load space/weight constraints, we might reserve only 500pcs
We then allocate and release for picking - but Epicor will always try and fulfill as much as it can against the order release, even if that quantity far exceeds the reserved quantity, so we may end up releasing 1000pcs to the warehouse for picking

Is this possible without getting into the nitty gritty of updating order line / release quantities? Any ideas gratefully received!

Thanks