I don't think "anything short of sin" is a good summary of 1 Cor 9 where Paul declares that he became "all things to all men". 2 reasons:
1. "Anything short of sin" puts the emphasis on the wrong side of the equation - it puts it on sin. If I were to teaching "anything short of sin" as a model for personal evangelism then it leaves my hearers trying to figure out what sin is in order to basically make sure they were not doing it. And when a lot of "sin" contains grey area upon grey area this is difficult. The bible says (Rom 14) anything not done of faith is sin, this perhaps combined with 1 Cor 9 suggests a better way of describing how we should evangelize. I think if you look at Paul's statements in 1 Cor 9 you see that a key phrase is: "bound to the Law of Christ" therefore I think what he is trying to communicate is not "anything short of sin" but rather "everything that is Christ". If by faith Christ would have you do something for the sake of His gospel then do it, and we can test this by the Scriptures because we have the very heart and mind of Christ. A good test I give young people who are deciding whether or not to do something that could be a bit "risky" for the gospel but are unsure is: "Would you be happy if Jesus returned while you were doing it?" I think "everything that is Christ" puts the emphasis on the right side of the equation and promotes people finding out who Christ is and to develop their relationship with Him in order to find the best ways of reaching people.
2. I think sometimes people use 1 Cor 9 to justify their worldly lifestyles. Some people want to be close to their past sinful lives for less than gospel motives... sometimes it is to prove that Christians can still be cool or whatever... At the heart of 1 Cor 9 is not Paul saying "Deep down I want to go and live like a Jew because I remember how good it was, and I will minister the gospel there." He is actually going to cultures and places that he himself would have been repulsed by - this is Christlike suffering for the gospel. So instead of using it to justify going to cultures and places that we enjoy we should be "becoming like the aged care patient to win the aged care patient, become like the disabled to win the disabled, etc..."

Becoming all things should encourage us to lay our own preferences down and live among those that repulse us in order to win them for the gospel. Anything short of sin seems to promote living the "sinlike" life you have always wanted to and have a gospel justification for it - this is not what Paul or Jesus did! They lived blamelessly among cultures and attitudes that repulsed them and they remained unaffected by them.

I say promote an "everything that is Christ" attitude to evangelism rather than an "anything but sin" attitude.