While not ideal, I did find some means to play DD Hor+. Here's the method:
1) Install the free Dungeon Defenders Development Kit DLC from Steam.
2) Find and run
..steamappscommondungeon defendersBinariesWin32DunDefDevelopment.exe in the Steam game folder. You can also add the .exe as a custom shortcut to your Steam client to enable the overlay.
3) On the first run it will tell you about outdated scripts that need to be rebuilt. Choose Yes. A console window will launch and process the scripts, taking about a minute. Close the console window manually when it is finished.
4) Launch the game via DunDefDevelopment.exe.
5) While in-game, open the console with the F1 key and type
FOV ### for your chosen field of view. In my testing this had to be performed only once per map.
The game seems fully functional through this exe. Even multiplayer works, though you cannot connect to retail .exe clients so you'll have to get your friends to use the dev version for MP.
Being a VAC-secured game, I wouldn't attempt a memory edit fix. Hopefully this information can be used to lobby the developers to put in an official fix for the retail version.