How I can manage having a lookup site column which reference a list inside a sub-site

Question

I have 5 sub-sites for each of our customers. and inside each sub-site we have a Issue list. now i want to create a new sub-site named "Projects" and this Project sub-site will have entries for all of our customers' projects. so currently i have the following architecture:-

1. /customers/customerA/
2. /customers/customerB/
3. /customers/customerC/
4. /customers/customerD/
5. /customers/customerE/
6. /customers/projects/

now I have created all the site columns and all the content types inside the root site (site collection level).

But now i am trying to achieve the following, but i can not find a straight forward way :-

1. inside the customers subsites' issue lists to add a lookup column which references the Projects list under the Projects sub-site.

but when i created a new lookup column under the root site, i was not able to find the Projects list under the Project sub-site. now i read that to be able to reference a list inside a lookup column, the lookup column and the list need to be inside the same site, while in my case i lookup column is inside the root site, while the Project list is under another subsite. so can anyone adivce what are the approaches i can follow?

i was thinking of this, to create a Mirror Project list under the root site, and using event receivers to be adding/updating/deleting projects entries based on the operations done on the real Project list under the project sub-site. then i can create a lookup column which reference the Mirrir Project lookup list.. now on paper this appraoch should/will work,,, but it will require extra efforts of having extra Mirror list + 3 event receiver which will be firing when users add/update/delete projects items from the real Project list under the Project sub-site.

Answer 1

Why not create the projects list in the root site and create a lookup column that uses this list? That way the issue lists in subsite can use the lookup column showing all projects.