Add lookup that refers to a different web site

Question

In Sharepoint, is there a way to programmatically add a lookup field that refers to a diffent web site?

In the user interface, when we are in a list A, and we are adding a lookup column we can only choose to get the informations from a list B on the same web site of A.
The only way I know is to create a Site column, but in this case the referred list B must be in the root site of the site collection. And this isn't a good thing in most cases.

Is there a programming trick (C#, VB or Powershell) to add a lookup field without that limits?

Answer 1

Add a event receiver on list B (list B can be in any site). On new item added / deleted, copy the list item on a list C (for example, lets say list C) residing where list A is created.

This way you can create lookup column in List A pointing to List C. On item/ updated/deleted in List B, item can be added/ updated / deleted programmatically in List C.

Answer 2

Finally I solved the problem using an overload of AddLookup method: SPFieldCollection.AddLookup In that method is possible to define a secondary web site for the lookup list: lookupWebId

public string AddLookup(
    string displayName,
    Guid lookupListId,
    Guid lookupWebId,
    bool bRequired
)