How to hide system info in HVM's to make nvidia driver work?

In qemu it is possible to use cpu flags to hide from the guest that it’s a vm. I’m experimenting with these flags in the qubes stubdom but no matter what I put there for qemu (different cpu models and kvm=off,hv_vendor_id=somerandom), the win7 HVM always knows it’s running in xen and the nvidia driver gives me code 43. What are other things that could “leak” the VM this info ?

qemu (different cpu models and kvm=off,hv_vendor_id=somerandom)

I don’t know what the Xen ones are (or if they exist) but the flags
above are for QEMU on KVM, not QEMU on Xen (Qubes HVM). They will be
ignored as the hypervisor and drivers don’t have any code to interpret them.

I checked the related xen doc page, and it says that the xen specific qemu doesn’t handle any cpu related virtualization. But it gives the board/machine type info to the vm, doesn’t it ? Besides that, is xen capable of doing such things that the original qemu does with those cpu flags ?