Well actually you can....
If you open two united mileage plus accounts and instead of your wifes name put your first initial before her name ie. your name david wifes name chana open one in your name and one in Dchana. (when linking the CO and united MP account they dont check whole first name just first initial.)
make sure everything else matches the continental info exactly and then link your respective CO and United accounts. transfer all your mile to their respective accounts, call united and ask them to consolidate the accounts.
this worked like a charm for me. YMMV