Add a feature to generate DC for the invoice which is already generated

Hi, it is been observed that if I have to generate Delivery challan for the items for which the invoice is already generated, I can not do that from the invoice itself, instead I have to generate DC after completely leaving the invoice option and then again have to fill all the details to generate DC for the same invoiced items. This is very tedious and duplication of work. Instead give DC creation option from the invoice itself so that if I want, i can generate DC once Invoice is generated and will not have to add all the details again. Do introduce this feature ASAP on urgent basis.