OH, I'm sorry this question slide right past me -- so flippin tired right now --- I had the very same question and don't know the answer. It says in the fine print on the coupon :
Qualifying purchase must be made in a single transaction and excludes taxes, tobacco products, gift cards, bottle deposits, prescriptions, lottery, alcoholic beverages, fuel, post office, photo finishing, video, 3rd party florist, Western Union and any other non-discountable product
BUT does the system know if you toss a gift card into your groceries? Don't know, but i'm pretty sure that's what we did the last time Metro had a threshold spend and it worked. We were planning on hitting up Sobeys tonight and i was gonna do the same thing but far too many things have cropped up for the weekend that i can't afford the 90 minute round-trip. Since the coupon booklet is good till the end of the year, we're waiting till another time to use those and I'll just get the gift card on its own next week.
If you end up doing this perhaps you can let us know how it worked out!