Sebastion -
The only problem with that approach is that if the track is blank, you will end up wth ' 00 '.
Instead of only selecting those tracks that require formatting, I came up with this approach:
Type: Format Value
Field: TRACK
Formatstring:$ifgreater(%track%,0,$NUM(%Track%,2),)
This way, the TRACK value is only formatted if it is greater than zero.