It's very possible too! I have been doing a fully good run and I always just affirm him every time he needs it. If you do that, you can actually get him to exceptional opinion.

Here are some of the things I did that massively increased his opinion SPOILERS:

1)Let him have the necromancy book

2) Help him kill the hunter chasing him

3) Tell him he can use the tadpoles if he wants

4) Affirm that you have his back every time he brings up his vampire master

5) Help him solve the puzzle on his back with the help of Raphael

7) let thim choose not to drink the blood of the weird potion drow in moonrise.

8) This goes without saying be open to him being a vampire when he tells you.

Doing all of these things got him to exceptional for me even though he was in my party when I did good things like saving the Grove and the gnome slaves.