If you get a nice pick up measure, simply freeze that track so you don't lose it.

Personally, I like to work in a DAW when it comes to mixing and production. In the DAW, it's easy to copy and paste to create the pickup notes, record it live, or use midi and a synth to get the proper pickup notes to start the song.

That's just my preferred way to do it.

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.