K+CAN Commander 1.4, ELM327 and STN adapters do not have a multiplexer. They only use the default pins. STN adapters (OBDLink, ELS27) and vLinker support additional CAN buses, but also do not have a K-line multiplexer. To overcome this shortcoming, you can use the cheapest $3 J1962 male-to-female adaptor. Using such an adaptor allows you to connect to almost any Control Unit if it is diagnosed via a non-standard K-line or non-standard CAN bus.
You can make multiple J1962 adaptors for different use cases. Examples are described below.