I am in the middle of building a skymaster f15 with tailerons only hence I don't need loads of channels and as I use futaba and have used orbit powerjacks before I wanted to use a 7009 with the futaba receiver but I want to have dual power supply to it but there is only one connection to the powerjack can I connect power via a spare servo plug port? what other options are there?

Not sure you can as the outputs give 5v to the Rx channels.

Spoke with Fletcher and he says booster is only on the signal, so you can run a separate supply into one of the servo sockets...

Use a PB sensor switch or Gemini II

i am using a 7.2v receiver and servos so every thing should take the voltage so I cannot see what could go wrong or am I missing something? I did want to use a gemini but how would I be able to make use of both outputs?

You may want to consider reading the Smart-Fly and other info on redundant power supplies to a single receiver. There are potential issues with connecting two batteries to one receiver's servo buss, especially if the batteries are not matched or the charges are not the same (e.g. the batteries will equalize via the Rxer buss.) Also if one battery fails, there is no mechanism to isolate the bad battery from the Rxer or the other battery.

Lots of people do connect two batteries to the Rxer buss. However that does not mean it is correct or even will work as desired. It can even introduce new problems. If it is large plane with lots of digital servos, then I personally would never consider tying two batteries to a Rxer's servo buss. That is why Spektrum has powersafe and there are products out there like Smart-Fly's Battery Share for other brands that did not consider a method to address the issue.

You wouldn't use the PowerJack. Just two outputs from the Gemini II (which are totally independent)
The Boost for Futaba Rx's shouldn't be needed in this case