don't do much pruning at all during flowering. if you can bounce some light in some how from the lower sides it would promote growth. it can even be cardboard lined with aluminum foil (dull side out). also, if the undergrowth doesn't really look ill, just underdeveloped, you could just wait for your first buds to mature (when half the hairs on the bud have turned dark colored ). some would advise against this, but it's obvious that buds on the same plant mature at different times. so harvest the first buds without uprooting the plant. this will allow light to reach the undergrowth and those flowers will reach their climax in potency. since you're growing indoors, the harvest time is unlimited, so this option is available. and next time you can keep the plant pruned during its vegetative state enough so that when it's time to flower, the secondary bud sites aren't blocked by thick primary growth, then hopefully all the buds will mature simultaneously and you can harvest the traditional way. cloning is sweet, I gotta start it. lates!