Running the CO2 into a powerhead is an effective method of diffusion. I have not tried it personally, but have read many accounts that state it works quite well. I have use limewood for a while, and I liked the results. I had the bubbles running under the outflow of my filter, and had positive results. I'd say your results with the limewood will be quite similar to the powerhead, but maybe a little less noisy.
Good luck with your findings