When The Witcher 2 came out, I was immediately put off by the inability to chug potions without kneeling and navigating a bunch of menus, making alchemy, a core part of the game, useless. Has this been changed in the enhanced edition, and if not, is there a mod the game to achieve this functionality?
This has not been changed in the Enhanced Edition. Potion crafting and drinking is still a process that requires that you meditate, which is not something you can do in the midst of battle.
Being prepared for battle before you enter it is kind of core to the Witcher series, so this is a conscious design decision made by the developers of the game. In the first game, this was balanced slightly differently - you could drink potions in a battle situation (although it left you vulnerable for several seconds), but crafting potions required that you meditate.
Meditation was limited to specific areas, such as fires in the wilderness (which you had to light using consumables) or in inns or other friendly establishments where it was safe to sleep.