Can you take advantage of Fizz data upgrade if you don't have data in your plan?

Steven yes but it will available just until your next billing date. If you have no data plan, you will however forfeit your rights to gift data and to receive gifted data. The exception is Perks, which you can use or gift with any mobile plan .

I'm doing the exact same thing at the moment, so yes! I pretty much have 1.5gb minimum constantly because of rollovers and perks