Patience, lots of patience, and very careful audio editing.

I submit this as an example: http://soundclick.com/share.cfm?id=13017714

I will often render multiple tracks of a given lead instrument to get several options because each track is slightly different. One of them may have pickup notes where the others don't.

The intro is a nice swapping of parts seamlessly. Starting with the fiddle and having the dobro come in to pick up the second part of the intro. Further on....Notice the solo transition from the mandolin to the fiddle. I needed the mando to complete it's part and in this song it left the part hanging for the next phrase...it ended up being a perfect hand off to the next player..... The fiddle came in with some pickup notes that worked perfectly for a transition.

The entire secret if there is one is to do surgical audio edits by zooming in and listening to where the transitions should be occurring. Let real band render as many tracks of the same exact track number as you need to get the results you're looking for. Edit the audio carefully. Nothing wrong with a copy, cut, and paste either if that works. I've done that more than once when the part I wanted in one place existed in a totally different place in the song.

In another song.... The Best Christmas (on my music website) the piano fills are comped from 2 or 3 piano tracks and the guitar solo in that song is a combination of 5 unique guitar track renderings and the extensive use of volume envelopes in Sonar.

Post a link to the song you're referring to. It's easier to give specific advice when there's an example to refer to.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.