Install GregTech.
GregTech's config file has an option to turn the mass fabricator on and off (off by default), and also an option to turn GregTech's own matter fabricator on and off (on by default), as well as configure said matter fabricator's energy need (16.6 million by default, 100 times that of the mass fab with scrap). You cannot configure the energy draw of the IC2 mass fab. The gameplay difference between the mass fab and the matter fab, aside from the configurable energy drain, is that the latter cannot work without scrap at all, and the recipe is significantly more expensive.
Keep in mind that this mod introduces a very large number of cross-mod changes, most (but not all) of which can be turned off in the config files. This does make the config files very large and daunting, too. I personally think several of the changes are very sensible, but that is something everyone must decide for themselves.
If you install GregTech, each of your users must also install it. If you change the config files, you should also distribute the changed configs to all of your users, or else their clients might display false information (the server still ultimately decides how things work, though, so it won't allow them to cheat).
