This makes no sense. I don't understand how everybody can so quickly come to the conclusion that CO2 is the best choice without knowing more about the tank.
What if he only has 3 java ferns growing in his tank? Would you still suggest getting CO2? There's always liquid carbon that can be dosed into the tank.
What if his 29g tank is TALL? The effectiveness of lighting is reduced depending on how deep the tank is.
For those of you who are saying to go with the lights, what is his 29g tank is LONG? Adding too much light to a tank like this can cause algae. Also, you have no idea what his plant setup is like so you can't say for sure whether they'd be able to out-compete algae.
Lighting, CO2 and Ferts need to be balanced properly for every tank. NO TWO TANKS ARE THE SAME! If you don't know what the current balance is like and how many plants he is trying to feed, there's no way to come up with a real educated decision on what the best option would be. All that you'd be doing is throwing random non-sense out about what you ASSUME his tank is like.
That's how I see it anyway.