Decoupling the ports from the switch won't help me. Those three ports share one link, maxing out at 1gbps. I need traffic to stay within the switch and out of software as long as the traffic is going to one of the relevant VLANs.
I can work around this by using a separate smart/managed switch, but that defeats the purpose of buying a router that has (according to the manual) a VLAN-capable switch built-in. A cheap-ass TP-Link can do what I need for almost a tenth of the cost, and it even has (poor) wifi support.