Just thinking out loud, the problem with having the dump in the centre for the throttle stick is that on most tx's the throttle channel doesn't spring back to centre, and if down is self right you need to be carefully not to manually pull the stick down too far as you will then just fire the self right valve. Ideally I guess you want it on a stick that does spring to centre so you can just quickly flick it up to fire and release and it will dump.
Not sure how the heavy guys get round this, I've always used the rudder channel to control flippers but it is a pain in the arse as I always forget which direction is fire.
In conclusion, I haven't really helped at all but hopefully food for thought!