Alpine kit with only 1 underseat sub?

[GizmoOG]

So I'm one of the unlucky people with the 2010 model bmw 1 series, which only consists of one underseat woofer, under the driver's seat. So my question is; How do I proceed with this? Do I need cabling from the HU to the subwoofer housing on the passengers side? Do I need to open up the HU? It's a lot of extra work imo.. I don't understand why they remove the cabling as well..

Thank you!