1. Splice together the signal wires from two Cateye or SigmaSports computers as shown at the Web site you referenced, running both captain & stoker's 'puters from a single front wheel pick-up. (Beware single-point failure; a bad splice or one that isn't water tight will cause both computers to go out as will a mis-adjusted pick-up: like when you put the front wheel on backwards, DOH!)
2. Run a Captain's computer off the front wheel using a standard length wire pick-up and the Stoker's off the back using a rear-wheel pick-up wire (usually long enough for stock tandems) with the pick-up head mounted just under the rim brake on the seat stay. Again, SigmaSports and Cateye seem to have the longest pick-up wires and most of the tandem dealers stock them, e.g., Gear-to-Go Tandems, Tandems East, Tandems Ltd, Precision Tandems, etc... (built-in redundancy; unlikely that both computers will fail at the same time).
3. A variation on #2 involves splicing together two standard-length or rear wheel pick-ups if you have a really long Stoker compartment or want to use a cadance pick-up. I have an old and tired Web page that describes how one of our two road tandems are set-up that fits this approach: http://home.att.net/~mark.livingood/...es/bc1200.html
4. Use a wireless computer for the captain with the pick-up mounted near the hub and a rear wheel pick-up wire kit for the Stoker, but run the wire to the front fork along the underside of the Captain's top tube. The distance to the front fork is often times a shorter run vs. the one to the rear wheel. This is how our travel tandem is set-up.
5. Use a wireless computer for the Captain with the pick-up mounted on the front fork and a rear wheel pick-up for the Stoker. Again, if you want a very tidy installation or have a really long stoker compartment you may need to splice together two standard-length or rear wheel pick-ups. This is how our off-road tandem is set-up.
6. Run both computers off their own individual pick-ups on the front fork; standard length for the captain and rear wheel pick-up for the Stoker. Similar to #4 but you end up with two wired pick-ups on the front fork. You can either put one pick-up at the front of a single fork blade and one at the back of the same blade on the same plane with one spoke-mounted magnet, or put a pick-up on either side of the fork and have two magnets spinning around on your wheel.
7. Use whatever you want on the front of the tandem and drop some major coin for one of Polar's wireless cyclocomputer/HRMs that have individual coding and then fiddle with the dip switches in the Stoker's rear-wheel mounted pick-up transmitter to boost the signal output: not cheap but if you already plan to get a high-end HRM for your Stoker it's not that much more $$.
Bottom Line: It's garage engineering. Just pick the method that you think will work best and have at it.
As you can see from my Web site, I use colored electrician's vinyl tape to hold Debbie's computer's wires to the underside of the top tubes which keeps them securely in place and also hides them from normal view. SigmaSports and Cateye use pick-ups that can be mounted along the spokes vs. some others that must mount on the hub and a simple, copper two-wire connections which are very easy to splice, whereas some of the other computers use wires that are not easy to splice; this is why I only recommend these two brands of computers for tandems/splicing projects. Any splices need to be water tight. In addition to shrink-wrap you'll also want to seal the ends of the shrink-wrap with clear silicone or hot -melt glue, otherwise you'll find that your computers stop working when you ride in heavy moisture or the rain.