Several years ago I did a blog post on the morality of sodomy as foreplay that got more attention than anything I've ever done. It was critical of those in the Theology of the Body camp who say sodomy is okay in marriage as "foreplay" as long as the marital act is concluded in the normal way.
Recently, the post got picked up by Ron Conte in A Debate About Marital Foreplay. Ron brings up great points and quotes from Church documents and the saints that were not addressed in the original article. He skewers the idea of some talking heads that ANYTHING is allowed as long as the marital act is concluded in the normal way and the couple agrees on the "foreplay." (Are whips and handcuffs included?)
I recommend the article. Some things are degrading and dehumanizing in whatever context they occur even if the parties agree.