When you say "vol" you mean volatility, correct? But you first said you suggest it be done by vol-weighting, but you now you wisely point out the risk of vol weighting. So I am confused ...or am I missing something?
You need to add some optionality/convexity to a passive portfolio construction if you want to beat the S&P; whether it be some ratio overwriting, simple CC or some sort of leveraged-ETF arbitrage. Beta or vola-weighting is pointless as you'll be constantly tinkering and who says it will beat? By definition it will fail (to beat) over the long-term.
I see your point about optionality/convexity. However, does that not expose you to greater risk? Also the aim here is not to beat the S&P, but to achieve a return in the range of -5 to 10%.