Based on the pattern regarding the replacement of sin with truth, what is the replacement for sexual lust?
My first thought that came after reading your question was a passage out of Philippians chapter 4. Verse 8 encourages us, "Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable - if anything is excellent or praiseworthy - think about such things." So, the opposite (or replacement) of sexual lust is to fill our mind with truth, nobility, righteousness, purity, loveliness, etc. In other words, fight lust with the truth.
We are also encouraged in Galatians to walk in the Spirit, and in so doing we will not gratify the desires (or lusts) of the flesh (Gal. 5:16). And we are told of this war going on inside of us between God's Spirit and our sinful nature (v. 17). But if we surrender to the Spirit of God it produces fruit of love, joy, peace, patience, kindness, goodness, and self control (that last one, self control, really addresses the issue of sexual lust well).
If you get to thinking about sexual lust it really is a form of lying and stealing. You are lying about God's design for sexuality by believing that sex was created for selfish indulgence. And you are stealing by capturing images in your mind of someone's wife, mother, daughter, etc. to use for self-centered gratification. So, in essence, you could take the same directives given in Ephesians 4 for dealing with lying and stealing and apply them to sexual lust. When lies about sexuality come to your mind you combat them with the truth from God's Word. When tempted to steal images for selfish gratification you instead work to offer a blessing to others in need.