I grow lettuces, both head and non-heading, but I'm not in the tropics. Your post made me think of a day several years ago when I went to a friends house and there in the ground next to her house were beautiful big cabbages and broccoli's, in June. I live in the south, outside of Nashville. Mine had long since been gone and I asked her how she did that and she replied "they're in the shade all day". I'm no expert and will never claim to be, but I suspect that cold weather crops are not only sensitive to atmosphere temperatures, but the temperature of the soil. I gathered from my observations that her cold weather crops hadn't bolted because the soil was still cool. I would absolutely give it a try, and my suggestion is to grow them in the shade. Maybe even try applying cold water from the faucet or a well, even if you're entering the rainy season? Maybe that's futile efforts. Yes I believe that heat makes them bitter. My fall lettuces and spinach being harvested in november and december are sweeter and more delicious than the same varieties grown in the same soil in the spring being harvested in may. As far as removing the outer leaves, sure, give it a try. If everything fails, you have gained knowledge through experience. That's what I love about failure.
