I had twins and the only way I got more than an hour of sleep at at time until they were 6 months old was by letting one of them sleep in a swing. I felt awful about it at the time, but you know what - it all turned out fine.
First, I stopped turning the swing on. So he weaned off the rocking. I also had it in the full reclining position, so he was practically laying down. I, like you, waited until he was about 6 months to make the transition, because I knew then I could let him cry some. Next I put him in his crib with blankets propped so he was in the same exact position as the swing. He did surprisingly well.
I would do some form of this - just gradually change the habit. Believe me, I dreaded it, but he did fine. At about 8 months he was still waking once for a feeding so I did cry it out and that was gone within a week.
Good luck - and don't listen to the people on here telling you you are a bad Mom. I asked my Dr at the time and he said the only bad part was going to be breaking the habit. Other than that there is nothing wrong with them sleeping in a swing. Of course, I would only do it if it is the only way. For me with twins, it was the only way.