MultiShop - Set Backoffice Domain from code

[Haegendoorn]

Hi,
I have 3 shops with different top level domains (.com, .be & .nl) I was modifying the mail alerts module to send e-mails with the correct links and some extra content (to the site they signed up)
All works well except for one thing, if a customer signs up for a product on the .com or .nl website. After some time the specific product gets back in stock, the customer receives an e-mail. In this e-mail the Message-ID and the X-AntiAbuse: Sender Address Domain properties are fixed on the backoffice that the admin logged into (in this case .be). How can I set the back office context from code?
Any help is appreciated,