I'll tell you what I just did recently (as in yesterday)...
I sent a letter to my first choice school and the whole letter was directed to the school saying why they are my number one school. I didn't have anything else to add by way of LOR, or anything. But I managed to include in the letter things that weren't mentioned in either my PS or DS about myself and why I think I would be a great fit for the law school.
Of course, I have no idea how this will be received. I guess my point is part of your letter should really state as to why Seattle U is your first choice. I also said in my letter that if i were to be admitted, I would be attending. It may seem desperate and you probably don't want to be as direct like that when talking to a girl you like, but I think for law schools, they like the attention..haha