I have had great results Nudibranchs as well! I have never heard of the freezer method before. Really interesting.... I suppose the risk is killing everything on the rock, some of which might be good?The best method I found was Lettuce Nudibranchs, they devor it like crazy so you need someone you can pass them on to when it is gone or they soon starve.
Another is raising magnesium to higher than normal levels. I have not done this personally but have heard of positive results from fellow reefers.