I need about 4 (5) mm extra space.
I want to use the WR-R10 for Radio AWL (control of flashes) and the HDMI for an external monitor.
I am not sure if the WR-R10b has sufficiently different shape from the WR-R10 that the HDMI cable would fit, and I know these are expensive bits, but it's a possibility that it might work. I would not buy the WR-R10b just to test it but if you can ask Nikon about this issue they might be able to say if it would fit better or not.
One alternative would be to use wifi to connect to a mobile device and display the live view on that. Software such as qdslrdashboard or Snapbridge should allow this (with quirks) via wifi. Also they let you remote trigger the camera but there is a longer delay than when using the WR-R10 and WR-T10.
Another approach would be to use the USB cable to tether to a laptop and there you could use Nikon's Camera Control Pro 2 or third-party software to display the live view, control the camera settings, trigger the shot and store the images. Other tethering software is also available but probably CCP2 has the most comprehensive control of camera settings.
There is also the Manfrotto Digital Director which allows one to use USB cable to attach to the camera and display the live view on an iPad. The product comes with a holder for the iPad (of different sizes). I am not sure if this product is still current. I think it's mainly intended for videography.