I have to agree with you. It took me a long time to abandon lust, but sure enough, once I realised that it was really wrong and had to stop, God helped me and now I am much more able to get rid of the thoughts that Satan puts into my head.
Although the Bible does not say that this act in itself is wrong, the lust involved is equated with adultery. I do think it would be possible for someone to think about their spouse the whole time, but really they may as well just come together as one flesh, just as God intended them to.
However, I do realise that every now and then, most people over the age of about 14 need to 'relieve tension' every now and then. What I am talking about is when a person starts getting ridiculous biological urges. The best thing to do about this is to ask God to get rid of them. However, it should be possible if you reach such a stage you can't cope with it anymore to 'relieve yourself' without any visualisation or lust at all. This could actually stop you from lusting as it would get rid of the urges.
One question: Supposing the married couple don't agree with artificial contraception and wish to avoid having children? Do you think it would be wrong for such a couple to engage in other sexual acts?