The API is more geared towards sellers using it for order and inventory management.
It is not so much a buyers tool.
Storing inventories off the site would be problematic as it wojuldnt account
for sales made between you taking the view, storing it then using it at a later
point in time.
As Sylvain mentions the wanted list and buy now tool do that in real time. You
can upload to a wanted list but i dont think it has an API functionality.