Show filtered customer_user list create ticket

[ghosthunter]

Hello @ all,

I've got a problem in listing only filtered values("From customer" [customer_user]) in "create new phone ticket".

The scenario is the following:

Our company have two business locations one in Poland and one in Germany. Both locations have two ticket queues for different topics.
Now my problem is that if one of the polish workers creates a ticket he/she must select a customer user and link it with the ticket but
they can see all customers, the ones of the Polish business and the ones of the German one. So I must filter the list in that way that
each business location only can see their "own" customer users.

My idea is to filter the customer_user via a mandatory id but I couldn't find an answer if this is possible and if it is how to realize it.
Maybe you can give me some hints or solutions to realize my idea.

I'm glad about every helpful answer.

Thanks!

p.s. I'm using otrs 3.2.6 prod and otrs 3.2.9 dev on a centos 6