04 Radiator change/ system flush

So I went down on my vfr and I noticed that my left radiator was leaking. I thought about letting my bike shop just weld it but I ended up buying a new one. I took my old rad off so now I want to flush my system before the new one, but can you flush with no left rad on? I don't know if flushing with new rad is okay or not because if my old one has a leak, will it even do a proper flush with the leak? Basically, do I flush with new, old leaking rad or no rad on?