Ken there are three ways of doing it.... maybe more :0
first, you can do nothing and make the blade and spring the same thickness.... trouble here is you get a folder that works but will get half moon scratches in the side of the blade from rubbing on the liners. works OK but looks bad.
Second, you can do as DeMo said and re leave the inside of the liners and create an island for the blade to rotate on and act as a bushing/washer. the relieved area doesn't need to be very deep, maybe .002 - .005 max. this works great but you need to have a milling machine to do it easily. I have seen guys use a drill press when in a bind.
Third, you can use washers. you will need to thin the blade by the net thickness of the washers you are adding. for example, if you plan to use .005 thick bronze washers, you will thin the blade .010 compared to the spring..... I happen to have the luck I got a surface grinder this past summer and it makes it really easy to do this, but I have done folders before that and used a disk sander and lots of coffee to get the job done.
there are a couple of wips on sight you can look at to get the idea of milling the scales or adding washers
Erik