This won't be much of an answer, but I hated to
see your question just dangle...(smile)|
Some MIDI programs, such as Performer, have a
feature where you can humanize a tempo by
tapping a beat as the file plays. If you have such a
program, converting the Finale file to MIDI and
doing it that way might be what to do.
If it must remain a Finale file, I'm not aware of
the ability to "humanize" the playback by tapping
in a reference tempo, but perhaps someone else
can help more.