You can add motion blur in post to the intended 24p sections , unless you were going for the fast shutter "strobey" look . Motion blur is calculated by examining motion vectors, so areas that move faster get more blur, static areas get no blur.

I think cuervo was referring specifically to the ramping: the transition between 240=>24 . Down ramping in software is either done using
a) dropped frames
b) blended frames
c) motion interpolated frames (generates new frames)

As atticus mentioned, the options in premiere are a) dropped frames, and b) blended frames. Option c) is normally done in software like after effects, twixtor, nuke etc... Older versions of Premiere actually had Timewarp as a plugin . Each method has pros/cons, but c) usually produces the best results. New intermediate frames are generated from motion vectors so motion is smoother (effectively you have more than 240 FPS to play with, so the ramping is smoother)