This is best done with the Dirtbike (Sanchez). On the first island you'll find a beach in front of the first safe house you're given. This will give you a long and generally uninterrupted straight line to work with.
I recommend switching your controller layout to "Classic" for this. What you'll want to do is start the wheelie then tap the X button in a rhythm to keep yourself in the same position. Once you get the feeling for it, do this for 30 seconds to net yourself the trophy.
If you're having trouble finding a Sanchez, there's a dirt track at the top of the second island that will always have one spawned there.