
I suspect it's probably possible to add this via firmware as I believe the signal routing is controlled by the on-board FPGA. But who knows whether adding support for this is seen as high priority.
If you don't need the camera control conversion features, you might want to take a look at the Decimator MD-LX which is a similar HDMI / SDI bi-directional converter. The key difference being that the Decimator MD-LX has several options for video signal routing, so in addition to Auto-Select (which behaves like the Blackmagic BiDirectional converter and changes based on the connected inputs), you can also set the routing to be fixed so that it doesn't change with loss of an input signal.