Well, it is possible, but with certain sacrifices.
There are... uh.... 16 classes to choose from in Kotor II. 9 are force power users, 7 are non-force users.
Now, here's the good news: You can make custom classes for Kotor II (theoretically).
The bad news: It seems any custom classes you make cannot have force powers. Apparently it's hard-coded into the game.
But, what you can do is change the names of the base Jedi Classes.
Jedi Guardian ---> Sith Warrior
Jedi Consular ---> Sith Necromancer
Jedi Sentinel ---> Sith Dabbler
I know, the names are ridiculous, but for example's sake, it works. The trade-off is of course that there would no longer be any Jedi-based classes.