I got Kelner to give me the quest by changing line 489 of z1311magidlg.txt (Windows version if it matters).
from:
Code:
begintalknode 34; state = 30; nextstate = 36; condition = (gf(177,4) == 1 || gf(170,1) > 14) && gf(167,17) < 2; question = "I am here to help you recover some records.";
to:
Code:
begintalknode 34; state = 30; nextstate = 36; condition = (gf(177,4) == 1 || gf(170,1) > 14) && gf(167,17) < 3; question = "I am here to help you recover some records.";
Edit: However, the dialog option shows up even after I complete the quest, so apparently that's not all I need.