The following article describes how to make CS5.5 use AIR 3.0 (instead of AIR 2.6). After following the steps in the article you will find that AIR still appears as if you were publishing for AIR 2.6, but it is really publishing for 3.0.
http://kb2.adobe.com/cps/908/cpsid_90810.html
Please read the disclaimer though. Adobe doesn't provide any support for this method of "updating" Flash CS5.5. But I can say I've followed the instructions carefully and that it works fine.
There is also this article - but instead of using the release candidates referred to in the article, use the actual Adobe releases instead:
http://priyeshsheth.wordpress.com/2011/10/05/how-to-use-flash-player-1 1-air-3-with-flash-professional-cs5-5/
Addendum:
Under Windows I was able to get Flash CS5.5 to target both AIR 3.0 and FlashPlayer 11 using the above methods. However previewing in Flash CS5.5 doesn't work, as it is using some other flash player for the preview. The published swf file is, however, fine. There may be a way to change what player Flash CS5.5 uses but I haven't pursued how to do that. If using Windows, an alternative is to use FlashDevelop, where you can specify the player you want to use.
