No, there is no way to avoid losing a stat point.
And as for the initial question, I always go and kill the mage to get the book of spells, and then I have myself admitted through the Pirate Captain.
If you have been admitted and didn't kill the wizard, you can do so later when you return from the Asylum.
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Melusine, High Queen of Fluffies, Archbabe of the Order of the Holy Flame and the Laughing Hyenas, &
Official Entertainer Elf of the BG2 Bar
Your voice is ambrosia