As stated above it has to be done on the phone.

I've done it when sitting with the other person and simply passed the phone across, but also I've had a friend call VS to arrange all the details then simply conference call me in at the last minute to give my authorisation to use the miles from my account.

You can also authorise someone permanently on your account, so your husband could authorise you on his and then you could spend the miles from both in the future - but still only over the phone.