Poor drainage is THE reason you are not getting them established. I have my blueberries in raised beds anywhere from 8 to 12 inches.

An equal mix of peat moss, sand and shredded pine bark is a popular approach.

I am not positive but I don't think it would be a good idea to add anything to promote root growth. Blueberries have very fine roots and are probably left alone.

Blueberries require ericaceous soil, with a pH between 4.5, and 6, in order to thrive. They also require constant moisture around the root. If they are watered with hard water, that is, water that contains dissolved limestone, then the pH will rise to 7 or above, and the shrub will no longer take up nutrient from the soil. Since much of Wisconsin has calciferous soil, and hard water, it is a challenge to grow blueberries successfully. I don't know if your soil is draining or not. You could dig a hole, fill it with water, and see how long it takes to empty itself. Getting the soil tested for pH would be helpful, and the tap water needs to be tested, as well. If you have access to rainwater, such as a rainbarrel, it would be best to use this water on your blueberries. Agricultural sulfur can be used to lower soil pH, but you need to know the actual soil pH before applying sulfur. We have about 20 blueberry shrubs, and they are all doing pretty well. However, there was some sign of iron chlorosis in a few shrubs this spring, and a few shrubs had red/brown leaves, in the early spring, that indicates they are not taking up nitrogen. I put down sulfur, and also put down water amended with vinegar, to lower the pH. They are all looking better, but as I said, it is a challenge to keep them green and healthy here.