Just find a spring that you think might work and use a small drill bit to drill the side of the steering nozzle so you can attach the spring.
Here is a pic of a Jet Ski Solutions start/stop switch and a bilge switch.
(If those start-stop switches are as unreliable as the bilge pump switches, then I wouldn't touch them with somebody else's 10 foot pole!!)
On the subject of circling SJs, don't forget that the water is rarely flat calm - surf, boat wakes etc. It doesn't take much to knock a ski to one side or the other and make it circle differently. I once watched my ski trace long lazy S turns heading away from me (and towards a rocky shore) as boat wake after boat wake knocked it from one side to another.
The moral is: if you're riding flat water in a confined area doing the kind of tricks that you can't do with a lanyard, then wrap it around the bars. If you're catching some air off boat wakes or out in the surf and you know you're not about to pull a 50-50, then wear the damn lanyard!! I hate this macho BS the seems to suggest that wearing a lanyard is for beginners. Consider this: if your motor stops as soon as you fall then:
1) It doesn't matter if your ski ends up upside down - it's not going to suck water into the cylinders if it's not running.
2) The ski doesn't drive off without you for ages. Think about it: apart from WOT runs (buy a couch....), how often do you fall far from your ski? If the motor stops right there and then you can get back on instantly. Would you rather wait for it to start circling, and then go round and round while you swim to intercept it? (They don't start to circle right away).
In my opinion the only legitimate reason not to wear a lanyard is for tricks which would otherwise be impossible (hood tricks, 50-50s, big throws etc.) or for competitve freestyle when your motor shutting down can be a disaster at the wrong moment.
My $0.02 (or was that $0.04...?)