Sending a specific keyboard shortcut to the host while the keyboard is grabbed by a VM?

I found several requests for this - some from years ago - but no solution.

I run virt-manager VMs on Ubuntu 20.04 host. All VMs use Spice for keyboard and mouse. Some use Spice for video, while some use Looking Glass.
On the host I have several static workspaces and I have setup custom keyboard shortcuts for switching between them. The custom shortcuts are not used in any of the VMs. Each VM window (either virt-manager or Looking Glass) is set fullscreen on a separate workspace on the host.
I want to be able to use the custom workspace-switching shortcuts to switch between the VMs in the workspaces.
The problem is that when a VM has captured the keyboard all shortcuts go straight to it. The only way to switch is to use the un-grab shortcut for virt-manager - L-CTRL+L-Alt by default - and then the workspace switching shortcut. I want to eliminate this extra step.