I do not suggest submersion of the leaves at all, just the sediment/roots etc.
ADA As works very well.
Sediment such as clay wetland soil worked very well too.
Capillary action, the sediments themselves, the moisture from placing a glass semi sealed lid on there etc allows plenty of moisture.
So you may go very low tech and cheap here if you wish, ADA As is certainly not required, however a nutrient rich sediment is.
Since there is no fish or water column, you can dose very rich, most hydroponic solution concentrations work fine. They are quite rich.
See here for standard "Hoagland's solution":
http://www.tre.umn.edu/teaching/Nurs...cture_2003.htm
http://fins.actwin.com/aquatic-plant.../msg01106.html
We have a long ways to go before we see K+ blocking Ca or NO3 melting any plant............
Some seem to think so however.
It's not the same as leaf exposure, but the concentrations inside the plant and the leaves as well as the root zones are exposed to very high concentrations in such solutions.
Regards,
Tom Barr