As for adding text - only SONAR option is into the lyric field (below staff view) - but I don't recommend as it is subject to hyphenation etc which would require a lot of messing around.
One easy way to do what you want, however, is to use a PDF driver as your "printer". (CUTE PDF is a free, widely available one, but there are lots available). In SONAR, set your printer up to print to your PDF driver, then use a recent version of Adobe Reader to add text, stickies, comments, etc to the PDF file, resave, print, etc. Note that SONAR "prints" the PDF file including your project title, you as the composer, etc, so you will only be able to add to the printout - but for quick and easy lead sheets it may suffice.
Hope this helps.