Tefilin for Bar Mitzva with Maaser money

Question

My brother-in-law is about to reach Bar-Mitzva. The family are not very observant but quite traditional. They are badly off financially. We'd like to buy him a good quality set of tefilin, as if we don't his family are likely to go for the cheapest option available. Tefilin are much more expensive than we'd normally spend on a gift like this. So far no one else is interested in splitting the cost with us as their present. Can we use maaser money for the difference between what we'd normally give as a gift and the cost of the tefilin. Thank you