[libvirt] libvirt qemu-kvm installation into custom directories

I am configuring upstream libvirt, qemu-kvm for development purpose in non-default directories. I want my upstream libvirt installation to use upstream qemu-kvm (and not the qemu-kvm supplied by the distro). How can I make libvirt to use this qemu-kvm for guest installations ? The Host contains other libvirt/qemu-kvm supplied by-default by the distro which I am not running but which I *do not* want to disturb. Please give me some pointers as to to do this. -- Onkar