HyperMac literally bought Apple adapters and chopped off the cable. I'm not sure how much more Apple-proof you can get than that. What you need to be is "lawyers on retainers who can keep draining your law funds"-proof.
edit: another comment suggest a MagSafe-MagSafe2 adapter is used. That's an interesting solution that may very well work if they require the customer to buy it themselves, as I believe the Apple patent hinges on using a magnet. Of course, they may want to argue that in court. For years and years.
Apple under Jobs might be different to Apple under Cook. Potentially they have Apple's blessing. Suppose a promising YC company was just going to make it for the newest Samsung laptop otherwise. What would you do if you were Apple? Just speculation, but that's how I imagine "Apple-proof" meaning, especially if there's some agreement that they can't announce yet.
edit: another comment suggest a MagSafe-MagSafe2 adapter is used. That's an interesting solution that may very well work if they require the customer to buy it themselves, as I believe the Apple patent hinges on using a magnet. Of course, they may want to argue that in court. For years and years.