Must admit I didnt use a metronome, I just concentrated more than anything on keeping my hand absolutely loose and relaxed, which as you probably now know isnt easy, I even practiced a lot not having my thumb touching the neck at all, I dont know much but I think it just takes time, it has with me anyway, keep at it and it will devlope on its own naturally. 

Try to get your finger tips to collapse naturally without forcing them which is a lot easier if your hand is very, very relaxed, dont fall into the trap that a lot of people do moving the wrist back and forwards while the hand doesnt really move, this gives the illusion of vibrato but produces virtually no discernible sound and is wrong. The hand basically pulls back while the fingers stay on the fingerboard in the same spot, this lengthens the fingers and causes the tips to faĺl.  Not much use to you but then again I dont know a great deal, except what worked for me, and pass it on:)