I don't think it'd be much fun being scum in a group of 1 with no communication.
Based on this idea, though, what about scum starting as a large group on D1, but as soon as the lynch happens, they split into groups of 2 which
each
have a kill (and are lovers, thus die as a group)? They'd still be winning together, but wouldn't have communication outside their groups (however, I assume they'd agree on a plan during the split in order to avoid accidentally targeting the same person with two scumgroups in the future).
12:4 (splitting into 11:2:2 after D1, with the two scumgroups independent but winning together) looks like good numbers; it's 25% (exactly) for town to win on D1, 34.286% for town to win after a D1 mislynch, leading to a total EV of 50.325%. 11:4 (preserving the setup name) has an EV of 51.810% to town. (All numbers assume I've done the EV calculations correctly.) The "every scumgroup gets a kill" mechanic was designed to allow large numbers of players without the game dragging out; however, it seems to suffer from the "you need a huge number of townies to catch a large number of scum" issue, with the 50% EV point for a 6-player scumgroup being at 27:6 (but with a reasonably good EV even for smaller numbers of townies, e.g. 18:6 still has a town EV of 42.987%.) As xyzzy suggests, making that White Flag probably helps (i.e. town has to lynch scum on D1, or else kill 2 out of 3 scumgroups after the split); 16:6 looks like good numbers for that, with a town EV of 51.239% (15:6 would have a town EV of 49.722%, so might be even better).