Hypersmurf
Moderatarrrrh...
The problem is that those who shoudl be best able to counter this trick -- skilled veteran warriors -- are also the least likely to succeed. IIRC, a Fighter and a Wizard have the same reflex bonus.
Monte's variant was Tumble vs Attack Roll.
If the attack roll beats the Tumble check, the AoO uses a separate attack roll, not the same one.
If I were going to come up with a Tumble variant and weren't concerned about making it a little more complex, I'd go with Monte's Attack Roll version, but use Dex bonus instead of Str bonus on the opposed check. The AoO attack roll would use the normal ability modifier.
-Hyp.