tell application "iTunes"
pause
set my_track to location of current track
set my_seconds to player position
end tell
tell application "QuickTime Player"
open my_track
set my_movie to first movie
set ts to time scale of my_movie
set current time of my_movie to my_seconds * ts
set rate of my_movie to 1.5 -- starts playing
end tell
Basically, this tells iTunes to stop playing the podcast, figures out where I am in the podcast, then tells QuickTime Player to start playing the podcast at the same place (within a second), but at 1.5 times the speed. Note that the pitch is unaffected -- only the playback rate changes.
I haven't done a lot of testing with what happens when you have multiple windows already open in Quicktime Player, so I could be wrong on guessing my_movie in the script. Feedback welcome!