When you need to move your handlebars up, install Sunlite's Chromoly Quill Stem Extender. One end goes inside the steerer tube and your quill stem inserts into the top. It provides 8 1/4 inches of rise and is compatible only with quill stems and steerer tubes.
This thing slips inside the steerer tube. There is no way to keep it from slipping. I have tried this in three different bicycles from three different manufacturers, and it slips in all of them. You would be better off and much safer just buying one of Sunlite's longer (or adjustable) quill stems instead.
Bottom LineNo, I would not recommend this to a friend