This doesn't sound like the question of a typical DN visitor, but I'm willing to offer a response, nonetheless.

I'm taking my answer from a Servant Book by Christopher West, entitled "Good News About Sex and Marriage." The author, whose book is judged doctrinally sound by the Church and who speaks across the country on the subject(s) of his book, says that the Church does not have a specific pronouncement on this question, although he is asked it many, many times. He does say (and you seem to instinctively know) that these acts do need to lead to intercourse--it's not an alternative TO intercourse. Why not? "It involves a severance of the pleasure of orgasm from the responsibility of fertility," writes West.  

West thinks that self-gratification is much more likely to be a motive in this kind of sexual activity and he thinks it's hard to keep from that temptation--to just get out of sex what makes YOU feel good. He also thinks that sometimes spouses push to get pleasure from the other spouse from actions with which they don't really feel comfortable. That certainly makes it selfish.