I feel your pain as two of the only three convenient, decent ones here went from 1x to unlimited -- and all 3 dropped Alaska Airlines participation altogether shortly thereafter. As for gift certs themselves: one of the joints works well for large amounts on a debit-style gift card; the second is part of the same debit-scheme, but the waiter was never able to get the card to load properly, so I gave up on that approach there after a few tries; the third one uses hand-completed paper cert forms specially designed by the owner. I did get a couple of $15 certs there for the just-ended Delta promo, to be surrended on future blacked-out Fridays. However, this guy is the one I have mentioned elsewhere who is hopping mad at RewardsNetwork. I don't want to push my luck with him after our conversation about iDining.
Since the upcoming NW promo is $15-per-visit there's not much you can do regarding your own 1x joint there, except enjoy the whopping 250 bonus miles each month. Sorry.

And a note about gift certs and 1x'ers ... I once ordered a paper gift cert, instructing the server to charge the total amount as one transaction. The manger delivered the cert after I surrendered my credit card. Surprise, surprise ... the server then presented me with two transactions to sign, acting helpless when I protested.