easy as pie. use raised beds with a solid barrier at the bottom. I would make mine 2 feet tall, but even one foot tall is enough for most plants.
the bigger hazard, compared to intake through eating veggies, is disturbing lead contaminated soils making lead dust airborne which you can breathe in and can be absorbed through the skin.
---> has tips on mitigating the hazard
please excuse the question, but reading the description of the land, Im wondering why you feel there is lead contamination, lacking actual tests?