Order Combining Ability?

I haven't managed to find such a thing after much searching, so I'll ask here and see if anyone is interested in doing in or has seen something that will.

Desired:
-The ability for a customer to choose to add the items in an order to a "pile" (the whole order, no piecemeal choices), with an adjusted shipping amount that will charge them only the difference between their already paid shipping charges and the cost to add the new items to the shipping total. IE, if they already have put three orders in their pile, and paid $23 in shipping, and they want to add another batch of items which would bring the total shipping for everything to $31, it will only add the $8 in shipping to the order.

-The combined order can be marked by the customer to either keep holding it, or ship their batch of items now each time they add to the pile.

-The customer can log into their account and view their pile .

-The customer can log into their account and choose to ship the in-stock items in their pile.

I can help with this. Please email back at abutani79@gmail.com to discuss further

Thanks,
Ashish