You didn't create this problem and the homeowner knows this if i'm reading correctly. I'd simply explain to the customer about that point being 10/100 and the ramifications which could be non existent in their situation and split off the Cat-5. My guess is that the customer will be happy with the end result.
I guarantee I'll tell you the truth and I guarantee I'll tell you what you need to know but I can't guarantee that I'll be telling you anything you want to hear.
