、。
If it's a request from none other than you, I can hardly turn it down.
Literal
Other not-being you [attributive-の] request [if-なら], coldly [adverbial-には] cannot-[suppositional-だろう].
他ならぬ is a fixed literary phrase meaning 'none other than' — it's the negative adnominal (~ぬ) of 他ならない, marking the following noun as specifically and emphatically 'that one.' 無下にする is a set phrase for 'to dismiss without consideration, to brush off rudely' — 無下 means 'cold, rude, unfeeling.' ~だろう softens the assertion into 'I suppose I can't.' Together the sentence has an old-fashioned, slightly literary register.