I've done this by focusing upon the nature and shape of our love. Like all of our desires and loves eros needs Jesus. Eros must go on a Christological journey for it to find its true end. Eros must become cruciform and be transformed into agape.
Here is Joseph Ratzinger making this point:
Love involves a real discovery of the other, moving beyond the selfish character that prevailed earlier [when we first fell in love] ... Love now becomes concern and care for the other. No longer is it self-seeking...instead it seeks the good of the beloved; it becomes renunciation and it is ready, and even willing, for sacrifice.
[Love is] a journey, an ongoing exodus out of the closed inward-looking self toward its liberation through self-giving...
[Love is] drawing near to the other, it is less and less concerned with itself, increasingly seeks the happiness of the other, is concerned more and more with the beloved, bestows itself and wants to 'be there for' the other. The element of agape thus enters into this love, for otherwise eros is impoverished and even loses its own nature.
I think this is the place to start with a progressive Christian conversation about sex. This is how to make sex mean more without piling on shame. Eros is an arena where we learn agape. Just like we're learning to be like Jesus in every arena of our life.
And this focus upon the shape of love can also bless conservative and evangelical Christians. For as we are embarrassingly aware, plagued as they have been with pornography, scandal, and divorce, conservative Christians marriages haven't been a real bright spot. This is mainly because the conservative Christian sexual ethic hasn't focused upon love but upon the When? and the Who? When can you have sex and with whom? What happened, in this attention to the exteriors of the sexual relationship, is what Jesus describes in the gospels: We clean the outside of the cup but leave the inside filthy and dirty. We've failed to speak about how eros isn't a playground of self-satisfaction but a training ground for service and sacrifice. We fail in making eros Christological and cruciform.
