This actually seems to have been fixed in the 1.5 branch: http://anonsvn.jboss.org/repos/jbossas/branches/Branch_AOP_1_5/aop/src/main/org/jboss/aop/instrument/ClassicInstrumentor.java See addHelperField()
[~]
$svn log --limit=3 http://anonsvn.jboss.org/repos/jbossas/branches/Branch_AOP_1_5/aop/src/main/org/jboss/aop/instrument/ClassicInstrumentor.java
------------------------------------------------------------------------
r106068 | flavia.rainone@jboss.com | 2010-06-15 19:33:03 +0100 (Tue, 15 Jun 2010) | 1 line
[JBAOP-796] Add an instance(Class<?>) to AspectManager and make woven code use that method instead of instance()
------------------------------------------------------------------------
r59554 | flavia.rainone | 2007-01-11 21:38:09 +0000 (Thu, 11 Jan 2007) | 1 line
Fixing Kabir's mistake
------------------------------------------------------------------------
r59532 | flavia.rainone@jboss.com | 2007-01-11 16:29:27 +0000 (Thu, 11 Jan 2007) | 1 line
[JBAOP-317] Task done
------------------------------------------------------------------------
https://issues.jboss.org/browse/JBAOP-796
Unfortunately there is no 1.5.7.GA release so you would need to build the branch yourself