It's not easy since Roll20 was build with the "one big HP pool" type of games in mind. You can however use the different bubbles above the token. First one for bashing, next for Lethal, last for Aggravated. Of course it's not perfect, but if each time you gain damage you also increase the bubbles to the left by the same amount, it could work. So say you got 2 Bashing, 3 lethal and 0 Aggr right now, then you'd write 5, 3, 0 into those boxes. Now you take 2 more lethal. Increase bashing and lethal by 2. That's7, 5, 0 now 7 in one box means the Wound tracker is full, in this case with Bashing, so he gotta roll for unconsciousness now (I think). If he takes another lethal now, you'd only increase the Lethal one, since Bashing already is full and now starts getting overwritten, so 7,6,0 Another two Lethal and it would spill over into Aggravated. 7,7,1. Lethal is full now too, which I believe is pretty bad even for vampires. Of course you could do it backwards too, starting at 7 and when you hit 0 it's full. As I said. Not perfect. But maybe better than nothing. If you had access to the API (requires Mentor level for the GM) you could write yourself a script that handles that auto increasing of the other bubbles and spilling over into higher damages automatically.