How to share firmware files across 2 macs for separate iPhones

I have had a hard time trying to figure out how to search this one. Seems I run into all that hacking crud when I mention firmware and/or IPSW files.
I have 2 macs and I want to conserver my bandwith. Each Mac has a dedicated iphone 4 to update. I have downloaded on mine and ready to update my phone. I want to get a copy of this IPSW file to her Mac so I dont have to spend the time to download again.
I am not sure how to approach. Any advise would be great.
--Mickey
iMac 3.0ghz 8 gb. Mac OS X (10.6.6) iPhone 4 - 32gb iPad 3.2