I also only use guano for flowering, but I generally make a dilute "tea" by mixing it with hot water, letting it cool, and watering with it. I tend to use fish emulsion and blood meal exclusively during veg (and synthetic chemicals if I notice a deficiency). I fertilize by making a similar tea, and have been very successful in the past. So, instead of adding it to the top layer of soil, why not just dilute it with water and feed as normal?