Similar to what reubent said, but using a different splitter and one less cable.
Use a pair of Y-cables (splitter) like this to connect the pre out/power in after the jumpers are removed, one for the left and the other for the right,
https://www.amazon.com/dp/B004EBX5GW/ref=psdc_172544_t2_B005DL2OVE
Then connect long RCA interconnects to the female connectors on the Y-cables, and run to the subwoofer.
Use a pair of Y-cables (splitter) like this to connect the pre out/power in after the jumpers are removed, one for the left and the other for the right,
https://www.amazon.com/dp/B004EBX5GW/ref=psdc_172544_t2_B005DL2OVE
Then connect long RCA interconnects to the female connectors on the Y-cables, and run to the subwoofer.