Throw a copy of iPXE on USB, then chainload it. Super easy. If you're using virtualization then there might be a chance iPXE is already used, in which case it's

Throw a copy of iPXE on USB, then chainload it. Super easy. If you're using virtualization then there might be a chance iPXE is already used, in which case it's super easy. Not sure if that changes much with Pis though, as they tend to be a different beast.