As far as I know this is a brand new trick never talked about before: How to get rid of the jet pack to take a picture of the green goo for my photo gallery and still pass the mission? Pretty simple, really!
When the mission begins, follow the train and kill all the soldiers. Then fly to San Fiero to the crane in Easter Basin and stand in the red marker. Follow the instruction to enter the crane. When you exit the crane, the jet pack will be gone.
Next, run over to the NRG bike under the hangar nearby and head to the train station across the street from the garage safe house and stand over the train tunnel. When the train pulls through, jump on and make your way to the container with the green goo and snap your picture. After snapping your pic, grab a vehicle and take the green goo to the Truth to pass the mission. Enjoy!!!