Leonard0 - 2:03 pm on Dec 13, 2010 (gmt 0)
In answer to the original question:
Yes, it should be possible to detect when ads are being blocked and serve your own.
Use an ad block/firewall filter detection script freely available on the web.
Make certain that it is working correctly, otherwise you could be blocking your own Adsense ads.
Serve ads from your own domain, from an URL that does not contains words such as "ads" or the name of a known ad server such as OpenX (phpAdsNew).
It would probably work best if you sell ads direct.