I’m going to be contrarian to a lot of this thread and say you should try just stretching. I can’t tell you if it will work, but the worst case scenario is that you waste a pretty small amount of time each week over the next 2–3 months but don’t gain.
If you follow this board for any length of time, you’ll notice that new members constantly post threads asking, "Can I do way too much to my penis, right off the bat?"—to which the experienced members must reflexively answer, "No. Don’t do all those things at once. Do the newbie routine and work up slowly." One of the principles around here is that you should do the minimum required to create growth. So it’s no wonder people are telling you to launch into the newbie routine.
But you didn’t ask if you can do too much. You asked if you can do less, because you have specific goals. So I think it’s totally reasonable for you to start with just the warm-up and stretching part of the newbie routine and see if it gets you anywhere. You should still start with a short duration (maybe 2 sets of stretches; 30 seconds each; up, down, left, right, out, and around) and work your way up. If you’re not getting results after 2–3 months, you can always start jelqing at that point.
Check out this thread for some good advice about stretches: Tricks And Tips For Manual Stretching
One thing that might ease your mind is that most people seem to have a much harder time gaining girth anyway. I’m still in my newbie gains, explicitly targeting girth because I’m worried about getting longer than I want, and I’m still gaining length twice as fast as girth.