Assigning successor to an item

Hi,
I am looking for a way to assign a “backward” like dependency, so that when a user is creating a new item, will also be able to enter another item that can take place only with the completion of this current item.
For example, user is creating two itemsitem#1 and item#2, both are activities that must be completed to allow work on item#3. But instead of going to item#3 and setting item#1 and item#2 as dependencies, I would like the user to build his project forward.

Thank you!
Baruch