Make them sign several clauses on a contract and send back a scanned copy. Really, if they still go through it without understanding what they are doing it will be on them.
Signed copies protect you from litigation in court, not loss of brand value in the court of public opinion. Plenty of people bitten by it will just never use a backup product from you again, and every time apple sneezes a flurry of journalists are there to document it.
I guess the idea here is to make enabling the option enough of a pain so that only people who need it are going to use it, and button smashers will be spared.
