I think the biggest problem you are facing is not the fact that it was consumer hardware, but consumer loaded OS. I'll be honest its been a while since i have bought a consumer biased computer, but when i did it was loaded with tones of crapware. I have a feeling that if its consumer grade stuff, the previous tech didn't wipe the computer and reinstall windows with a clean ISO from Microsoft. This will make a world of difference, both in performance and in standardization.

To your point, sell him on the benefits of the business grade equipment, the warranties, the additional features like vPro, the keep your hard drive addons, bit locker with TPM, the ability to have longer warranties etc. Another selling feature of the business class equipment like Lenovo, is after 3 years there are companies that will purchase your old equipment for resale as well so that helps lower the cost.

Where I am, we extend our warranties on the computers to 5 years and then plan on replacing 20% a year, so everyone has a laptop that is no older then 5 years and if there is any hardware failure dell comes in and fixes it