Hopefully others with more knowledge will reply, but I THINK the only way to slow down the tempo during playback is by setting panel memories with the same voices, but different tempos ... not exactly the smoothest way to accomplish this ...

After the easy record, I believe you can then go in and during playback do a 'realtime' record for the tracks/voices you want, and just add them in the measures you want them ...
Good Luck ...
t.