As someone who uses LGW-GCI regularly when going onwards to ACI, I'm not really sure what you mean. It really is pretty seamless these days. As a Guernseyman, I wonder how you avoid Gatwick when connecting given that it is by far the most convenient option?
I've given up on Gatwick as I can't remember the last time when I've used it during the last ten years when there hasn't been some building/restoration work going on, and the security goons make travelling through there a fairly unpleasant experience. Having to negotiate the car park laughingly called the M25 makes onward travel a lottery when trying to catch onward connecting flights out of Heathrow. Travelling to Alderney from the UK you would be quicker routing direct through Southampton that would be a lot more convenient.