For the employer thinking about keeping the miles, I think its all a matter of accounting. I assume that your employees either charge the tickets and submit expense accounts or the travel department or secretaries make the reservation and give their boss's FF number. Consider changing your travel requirements so that the tickets are purchased by the XYZ corporation that has a FF number & that corp gets the miles. For the kind of business I assume your'e doing, I'm sure every one of those airlines would kill to set it up for you.

Not that I advocate for that policy.