Sweet. I was able to get Persona 3 Portable to replace Patapon.
You need to download
SignTool.
Agh here we go.
You download the .pkg file of your base game from
this list here. Then you unpack it with
PKG Decrypter. Then open the folder of the decrypted PKG and go to USRDIR, CONTENT. Take that eboot file and place it in the same folder as SignTool. Then rename the eboot to NP.PBP. THEN, move the iso of the game you're trying to get on your Vita on SIGNNP.BAT (It won't work if the directory has a space in it. My username on this pc is my first and last name, so I had to move SignTool's folder to my C directory.) THEN, when the process is finished, go to the FIXGAME folder in SignTool's folder and there you go bud.