Change request site at arrival

Change request site at arrival

By default, a request is routed to the requesters site.
If an external requester can serve multiple sites, but they are assigned to the default site upon their first request.
This causes the following issues:
  1. An requester from Site A cann't send a request for Site B.
  2. An external contact is assigned to the default site upon their first request and can no longer submit requests to other sites.
Can this default behavior be customized?
We’re thinking of having a dedicated email address for each site.
The site for the request would be determined by the reciving email address.

This way, all data for a single location (assets—synchronized from Endpoint Central—users, and requests) stays together.

We looked into a solution using groups.
This could be a solution, but it doesn't keep all the data together.

Another option is to use multiple Service Instances; we want to manage all locations from a single instance so that administrators aren't tied to a specific site.

So is there a solution for this issue?