I don't know about making the foam hard, but otherwise, many folks have tried similar things. Adding sugar might be a better approach since it is purer than vodka.
When I dosed sugar once, many of my corals turned brown. Probably zooxanthallae growing much faster.
One thing to be concerned with is low oxygen as the bacteria use O2 to metabolize the ethanol (or sugar).
So whatever you do, start very slowly.
In general, growing and harvesting macroalgae is likely to be a better approach. These articles describe other approaches:
Nitrate
http://www.advancedaquarist.com/issu...t2003/chem.htm
Phosphorus
http://www.advancedaquarist.com/issu...t2002/chem.htm