Conform tempo to Live-Recorded Midi Performance

I recently recorded a live performance of a piano piece that has natural changes in rhythm.  As a result, the notes do not line up with the lines in the piano roll view.  Is there a way to easily conform notes to those lines without changing the sound of the music in order to make it easier to add accompaniment?  I thought this might consist of recording a new beat track that would indicate the tempo of the recorded performance and the system could conform the tempo to match the natural changes, aligning the previously recorded music to the lines in piano roll view, but obviously, I don't know how to do this or if it is even possible.

Thanks so much for your help!

Thank you so much!  I actually wasn't aware of the audio snap feature in Sonar (newby, needless to say).  While I can definitely see what you mean by the feature being limited, I did get it to work to a degree and make my work MUCH simpler.  I ended up playing back the midi performance while recording myself tapping on a microphone with one loud beat and 3 softer beats for each measure.  When I applied audio snap to this, it aligned my midi file pretty closely to the measures in piano roll view and allowed me to add notes visually.  This was a lot easier than trying to place notes and keep playing back the music to check for alignment.  Thanks again for making my life a lot easier!

What you did was perfect. Smart thinking.