In my original video on using the ACW (long ago) I mentioned this. Sometimes you have to use your head. If the ACW thinks it is 144 BPM and you know it should be 72, tell it so, hit play and then hit the F8 key a few times on the 1 of each measure.
The ACW starts looking ahead for peaks and within a few bars usually has created a tempo map at the desired tempo pretty accurately.

Before sending back to RB I suggest listening through t once while watching the bar markers and adjusting as needed (to avoid having to go back later, which always means regenerating any previous work) .
Note the option to cut tempo in half ..

http://masteringmatters.com/stuff/ACW_Tempo_Map_creation.avi





I do not work here, but the benefits are still awesome
Make your sound your own!