If the manual doesn’t describe such a method, then it probably doesn’t exist. In that case, I would contact club-3d email support directly.
As for the limited number of ports, I would consider adding a USB 3.1 hub. One nice thing about USB 1.1/2.0 devices is that they are completely separate from USB 3.x devices (different wires).
Before doing that, there’s a couple other ideas to try:
What happens if you switch the mouse and keyboard in the USB 2.0 ports? The installation guide seems to indicate that there’s no difference between the mouse and keyboard port so probably there’s no change in behavior but it’s worth a try.
Most USB keyboards can act as a USB hub (they have one or two downstream USB ports). What happens if you connect the mouse to the keyboard? Maybe the mouse traversal functionality will be eliminated if there’s a hub between the mouse and the USB 2.0 port of the KVM.