10x once again stack overflow for the flood of answers i got while all the idiotic questions are being answered...
i didn't find a way to do it, but i use the following a separate gradle file with a class that encapsulate finding the aapt and running it, then i use apply from: 'xxx.gradle' and in the included file i use ext.aapt= new AaptRunner(); then i can use aapt object in the original build script.