just putting sand over the top of your plot isn't going to do much, so you're better off just digging your own holes, and use your own compost/soil mixture. the dirt being very acidic and clay being all over the place will stress the plants out quite a bit, but what i did was made a compost tea and top dressed my plants with a low ph compost which helped out alot. if you layer the bottom of your hole with crushed stone or just smaller round stones, this will help drainage in areas where there is more clay in the soil. It would be pretty hard to not disturb the soil too much, and still come out with quality plants. I know people that just planted in 5 gallon pots outdoors and it makes it easier to move them if you need to also. are you making one big plot, or individual holes for each plant?