Is it permissible to congratulate and bless someone who has bought a house through a bank loan (usury)?

Purchasing a house with an interest-based loan is Islamically forbidden (haram (definition)), and one must repent from it. Whoever is connected to the buyer should advise him to abandon this act. However, congratulating someone on acquiring a house is permissible, because the congratulation is directed towards dwelling in the house, not towards the interest-based contract, and the object (the house) is amenable to blessing. What is forbidden is naming or blessing something that is intrinsically forbidden, not something forbidden due to an external factor.