I can see that in virt-manager that when I click 'Add Hardware' for a particular VM, I can add a Smartcard. Looking at the documentation for libvirt's domain XML, it looks like you could try adding a smartcard element to the devices section:
<devices>
<smartcard mode='host'/>
</devices
https://libvirt.org/formatdomain.html#elementsSmartcard
The documentation suggests that mode host should send all requests from the guest for that device to the host via NSS. Optionally it seems you can specify the controller, thought at the moment it says only a single smartcard is supported:
<address type='ccid' controller='0' slot='0'/>
Regards,
Tom
