The OP mentions Giant Eagle, a grocery chain here in western PA and eastern OH. They have a "fuel perks" program, ten cents off per gallon for every $50 spent. You can buy the Universal gift cards at GE and get the fuel perks, so that's likely what OP is after.
I'd like to know the answer as well - a thousand dollar gift card would provide up to a $60 savings ($2.00 off a gallon, 30 gallons max per fuel up), for basically no cost assuming you pay off the gift card right away.