Not that I'm aware of. I added another user to my card, but I didn't get any bonus for it.

What may make better sense is to have your wife apply for one herself (she gets the 30,000 miles in her name) and make sure she gives the rep the referral code so you get the referral bonus:

I just googled this:
http://www.bankingdeals.com/united-m...o-30000-miles/

On the United website, I think the referral bonus is only 5000 miles. I've seen the 15,000 referral bonus miles floating around before, but I'm not sure whether those are targeted offers (I don't believe so).

The only downside is that your wife would need to pay the annual fee (whereas a companion card would be free - no additional annual fee).