根据《牛津英语用法指南》的观点：……在有礼貌的请求中，一般不用 were, 而用 would be。如：

We should be grateful if you would be so kind as to let us have your cheque as soon as possible. 如蒙尽早将支票交来，我们将不胜感激。 (不能说：... if you were so kind...)

We would appreciate it if you would be so kind as to let us have your cheque by return.  如蒙即送支票，我们将不胜感激。