4. Click the Clip Follows Project button.
IMPORTANT! Be sure to click the drop down to the right of this option, and set the mode to Auto Stretch before enabling it. Otherwise SONAR will automatically snap the clip's tempo map to the project's timeline in addition to enabling auto stretch, which is likely to have undesirable consequences.
Also, be aware that stretching audio more than a few percent on something "fragile" like an acoustic guitar part is likely to produce more audible artifacts than most critical listeners would tolerate, even after rendering with the appropriate offline stretching algorithm (see Render Mode section of the Audiosnap Palette).