When I found the Remnant gate array system I slowly captured all systems around it until it was safe from other empires. Then I designed and built a long range artillery system around every planet in every system surrounding the gate array system. Two or three on each planet in fact. The artillery stations had plenty of range, enough to hit anything within the Remnant system.
Then I began to slowly seed scouts into the system to get eyes on it, selecting my artillery, pausing it and bit by bit selecting every single enemy in the system. It took a while but I was able to win a flawless victory, picking apart their defences and fleets with concentrated long range shelling.
Very tedious but oh so satisfying. It is still my super duper extra special probably never going to happen happy wish that artillery stations can spot targets outside the system they are in... because I like to turtle and because my long game strategy uses these artillery stations it can be very tiresome having to manually fire them, I just wish they could pick out and fire on targets of a certain size anywhere within their range freely.
I understand why this can't happen, but hopefully with SR 2 who knows