I don’t know much about what is and isn’t made available with Apples iOS SDK, but you may try simple using the iOS device to map the network strength as you wander around and then sync it with the Mac for other features. Of course that is probably the main issue that you’re having, because putting together the rest should be relatively easy.
Thanks for a great product. I haven’t looked quite yet, but you should have a Paypal donations button somewhere on your page. Keeping the app free, but requesting donations would be mighty fine of you, and you would definitely get my money..when i have a little to spare.