Inasmuch? Simply write your code, compile it as an .swf and embed it in an AIR-Application. There's no difference to Flex-Apps.
There are many ways to do this. As long as you can compile the Actionscript code to a SWF file, you can then package it into an AIR file.
If you ask how to do this in Flex Builder, at least in 4.0, when you create a desktop app. project. In the last dialog, there is a row says
main application file, change the default file extension .mxml to .as, then FB automatically create the project with an actionscript package.
Then you can start to code in actionscript without using Flex.
Hope this answers your question.
Hello, you can just use Flash CS5.5 and publish for Android / IOS as you want.
And AS3 are more fast than Flex + MXML
If you want exemple, just tell me