EasyRPG Player has an experimental feature that will opt-in for the RPG Maker 2000 Battle System while running RPG Maker 2003. So you get all the 2k3 features except for the battle system.
The setting is lost everytime you edit the database and you must manually set it, e.g. with lcf2xml.
Important: Make a backup of at least RPG_RT.ldb before doing anything of this!!!
How to use it: Put it in the game directory, then drag & drop RPG_RT.ldb on lcf2xml.
Open the RPG_RT.edb in a text editor. Search for easyrpg_use_rpg2k_battle_system and set it to 1.
Save the file.
Drag & Drop RPG_RT.edb on lcf2xml.