Hi,
I only know the "wrong" way to enable experimental lpes: uncomment the line
#define LPE_ENABLE_TEST_EFFECTS
in src/live_effects/effect.cpp. The right way is via some switch in some config file but I'm not sure. Under windows, I think it's a matter of changing one line in build.xml...
*BUT*
These effects are in fact experiemental: only use them for testing/debugging/commenting. An experimental lpe will almost surely undergo deep modifications before it becomes non experimental. Either the very definition of its parameters or the way it is rendered might be affected, and in both cases all art work based on it will be lost! So use carfully. (and of course, if you enabled experimental lpes in the "wrong" way, don't forget not to commit this change to svn!)
Some lpes are in good shape however. What is needed to enable them is a good collection of tests cases... So if your favorite lpe is still hidden, consider supplying a test file for it. jfb.