I'm not familiar with the exact sound you're describing, but it might be possible to achieve something close. After some trial and error, I got the best results with the Glide knob at the 10 - 11 o'clock position, the Glide set to Rate mode in the settings, the PB set to Unison mode, and the Voices > Master GlideTime set to a moderate negative amount. At -35% the effect is obvious but not very musical. At smaller amounts it gets more subtle, though as with everything on the Polybrute, it's a little unpredictable.