I did it. My Spartan now has a sparking wheel <img src="images/graemlins/grin.gif" alt="" />. The knife still needs some serious cleaning and the scales could use a better finish <img src="images/graemlins/blush.gif" alt="" />. I post now anyway before I have to dig up a long forgotten thread to do so.
The sparker uses ordinary lighter flints. This should make it easy to aquire replacement.



The old scales where warped beyond repair so I decided to make new ones. I used aluminium as it´s more stable than plastic. The scales are snapped on just like the plastic ones. I went for a two layer design for the scale with the sparking wheel as it was easier to build. The layers are held together with the two screws on the left. The third screw holds the sparking device.
Here´s a picture of the sparking wheel:



The main body of the sparking device has a 6 mm square cross section. The rib is 3 mm thick and slips under the upper layer of the scale. It has a hole with a M 3 thread and there is sufficient room for pockets to hold spare flints (I haven´t made those pockets yet).
The sparking wheel protrudes enough for spinning and does not impair the use of the blades. The flint and spring are inserted from the bottom and are held in place with a headless screw. The screw can be used to adjust the pressure on the flint. The spring and the sparking wheel are scavanged from an empty BIC. I forced the zinc discs off (that is easily achieved with two pliers) to reduce bulk.



The best way to use the sparker is to hold the knife in the fist and spin the wheel with the thumb. Due to the design it´s hard to spin the wheel in the wrong direction. At least with the Spartan the wheel can be used with the left hand.
I tried cotton balls and cotton balls with vaseline. Both could be ignited with the sparks.
The device could be used without the SAK but it´s hard to hold. I rate the device as adequate for fire starting. I think that it could be really hard to operate with cold hands or gloves. It requires tools to replace the flint and replacing the flint can be difficult as there are small parts that could be lost.

Conclusion :
Adding a sparking wheel to the SAK is feasible. It adds about 3 mm of bulk. The small size makes use hard in certain circumstances. The intended use of the knife is not compromised. The sparks are not great but good enough to ignite good tinder. I would consider it a novelty item. I would not rely on it as a primary means of fire starting.

For the curious:
No electro powered tool was used to build the scale and the sparking device. I used a hand powered drill, a saw and a couple of files (mainly 10" #1 and #3 and a 4" square #3 for the wheel slot)