from what i've heard that the chance you'll get multiple items will increase if you stand as close as possible to him and click as fast as possible. so what i mostly do is jump to it, and click while jumping.
Btw the rumors about that you can get a DB with the blue mouse quest is true~!! I never believed it untill i got a db.. If you'll get a db, then you won't know it untill you exchange the items tough. Cuz when i got my db i just had normal items, was exchanging my items in tc, and i had like 3 pairs of all items and lots of loose items, first pair gave me 9 mets, second gave me db, and third gave me, and third mets again. I only had this once tough lol, hope it'll happen again soon