Both methods are OK but what if you could tap the tempo with your foot while playing, and use that info for feeding method #2 ? That should give you the most accurate tempo map since you were tapping it as you felt it while playing your part, instead of trying to recreate it afterwards.
[EDIT] I re-read the remainder of Dirk's post, and while the following method is basically the same, it does everything in realtime without having to duplicate the track then delete stuff etc. ;) )..
Well of course nothing prevents you from doing just that!.. provided you had a spare pedal that you can operate from your left foot (presumably, the right foot will be busy playing the piano's sustain pedal ;)..
You would open a 2nd MIDI track for recording, and use the Input Transformer to filter out the left pedal on the incoming piano track, and another Input Transformer on the 2nd track, filtering out everything except the left pedal. You would also use a 2nd module of that same Input Transformer, to convert that left pedal into some arbitrary MIDI note.
So at the end of your recording, you have both the piano Part and the tapping Part, all in the one pass, ready to perform the remaining steps in method #2 ;)
you are a true gleaming gem of these forums!
( and thinkingcap, too )