This is the info Dave at Action was kind enough to send to me...
"Craig Talbot did come up with a jet-drive unit and sold a few prototypes to Ron Dean but the thing was never brought up to full ACTion spec. We certainly didn't inherit the circuit for it when Craig passed on the business to us. We'd have made one ourselves but there is surprisingly little demand.
It's not a huge job to arrange for a servo on a Y-lead to lower the thrust bucket when you pull back the throttle stick; the better alternative is to have the thrust bucket on a 2-way switched channel and to raise and lower it before you apply any throttle. The big headache is that the ESC needs to run in the same direction both ahead and astern. We can easily modify a P80 to do this but it's only good for 20A continuous.
Hope this adds a few grains to the heap of wisdom!"
On the one I'm just finnishing, and Atlantic 21 with one jet drive, I have the reverse bucket on the switched channel 5.
However I find that the reverse is not very effective, and just running the motor in reverse is nearly as (in) effective. The boat turns on a sixpence and reverse is not really needed.