Don't forget you'd end up paying the taxes etc for two people. This may not be insubstantial, depending on where you're going. So if you don't want to do a trip, my advice would be to let it go. The miles won't expire for a long time (and not at all if you keep earning). Just use the next voucher when you can.
I think I had to throw away my first two Amex vouchers, and nearly had to throw away one that was expiring this month, too - which would have made my Amex voucher use a measly 50%.