First heard about the idea when Buzz T. described using cork to build up spool arbors. Ran into graphite arbors* Light bulb went on! Mark G. threw in some scientific and practical fertilizer. Dremel did the rest. Voilà, poor man's wiffle spool!
* Graphite arbors are used in rodbuilding as spacers between the blank and the reel seat. They can be described as rigid foam pieces. They are extremely light (about 2/3 the weight of cork) and very easy to work with using sandpaper and/or a Dremel tool. They are available from Cabela's for $2.79 for six in the sizes that I favor for Curado 100 (G22) and 200 (G24).
Using this material to build up the arbor decreases the total weight of the filled spool, with attendant lowering of inertia. This benefits the efficiency and controlability of the reel in the same way a classic whiffle spool does - for a small fraction of the cost.
Curado 200B spool + G24 arbor
<=The cut doesn't even have to be perfectly straight, since the two halves will fit together exactly anyway.
<= A very thin coat of rubber cement on the spool is enough to hold the arbor firmly in place after line is added. The flat spot on the arbor gets evened out as soon as you put a few wraps on.