You may want to look at Noodler's web site. He used to have instructions on how to adjust the in flow on his pens.
Also, I believe that the Preppy can be converted to an eye dropper fill with the addition of an O-Ring and a little silicone grease. Noodler's used to supply them this way with some of their larger sizes of ink bottles. The only problem I've had with the Preppy is that the pocket clip tends to break off after a while.