The easiest solution is also the most practical for guest flow and operations. Shorten the river to a small loop around the main part of TSI. Fill in the back half and level the Fort island. Put Cars on part of that, and then Villains on the rest and in the woodland behind HM.
View attachment 847738
Now you have a full loop around the river, removing the dead end at BTM, and both Cars and Villains all inside the berm. Add a path to Villains next to HM and one in Fantasyland (theme that one to the dark forest from Snow White) and you’ve got plenty of ways to get around for guest flow! Only flaw is not having an exit point for the Riverboat whenever it needs repairs. Maybe you could have a river just wide enough for it running between BTM and Cars out to the current exit point?