Not truly a "Hack". EAC lets you call many sorts of conversion engines after it rips to a wave. To make MP3s you download the Lame engine and point it there and to make FLACs you download the FLAC engine and point it there. The trick is that not every setting for flacks is presented in the GUI so you need to add a few command line parameters for things like your file name preferences.
Short instructions showing the process with screenshots. Basically, it's download & install FLAC then do this.
Save all your settings as a profile. Then you can load your MP3 profile file as needed then switch back to the FLAC profile as needed.
Now if you want it to automatically do a flac then an MP3 in one button push, it gets trickier but honestly, there are easier tools for that.
I use EAC because it's complexity tricks my brain into thinking the music will sound better. heh hehehe heheh
