I usually just drop the wort into the bucket from a few feet. I know it's not ideal and I plan on getting an O2 system later, but I'm not sure aeration is the cause of your "underattenuation". Do you brew with extract? Your fermentability may be limited to what the extract company makes it. There may be too much sugar left over that the yeast can't eat. If you are shaking, you are probably getting more O2 in your wort than I am.