Well, i had to change my system...After all i was going to use a lot of Scrolls because our mod will feature (when it's released on some veeeery distant day) a lot of Recipes and Runewords (hopefully). Therefore, if you do one different kind of item, and make them all gambleable you'll find it hard to gamble anything else but those scrolls...
So i had to switch to the unique system...
It took a while to figure it out, but when you set the "magic", "rare" and "normal" columns in "itemtypes" to 0 then you seem to be able to gamble unique scrolls at a 100% success rate unlinked with the dll...
Somewhat strange, but if it works... 
Only when you would gamble a scroll double, then you get a normal one that does nothing. (The game seems to reset the unique gamble count upon leaving town, so gambling several times in a row cannot provide you with doubled scrolls)
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i am breathing the fire
it's kiss is my desire
i am preaching the flame
you wont be the same
now you will burn
back you can't turn