To atone for my error, I did some poking around and found a good summary hack of the display ads network (AdSense) that gives you some options.
http://www.makeitbloom.com/blog/advanced-mobile-targeting-in...
You can also use the retargeting feature in GA to help convert people once they find you. http://www.lunametrics.com/blog/2012/07/30/adwords-remarketi...
You can use "device" as a proxy for OS though quite substandard.
A slightly more elegant way to do this is to do a device specific landing page. http://searchengineland.com/new-valuetrack-features-for-enha...
Given Apple's poking at Android, my sense is that Google doesn't have a real interest in helping Mac People find each other. Sorry for leading anyone astray.
It's also really got me wondering why they persist. I'm assuming it's because they'd make more money this way. You pay for "BS" windows clicks, given Apple's 7% OS market share (non mobile). The same way they closed the tablet arbitrage (you now have to pay desktop PPC prices for tablet.I bet if Mac users gained share over windows desktops that would change, like they had to in mobile.
One way to thwart them would seem to be to focus on paying per conversion, and using retargeting. But I'll let others with deeper mac marketing experience than me, add value here.
Hope this helped.
https://support.google.com/adwords/editor/answer/1211190?hl=...
Note also that most A/B testing networks can be used as defacto Ad Serving/Dynamic content serving because you can target operating systems as well.