hi
i guess that there is a way in FL, but i'm currently @ work and not at home so i can't actually tell you how..
but there is another way (how i used to do it). i exported that part as a audio-file and edited this in cool edit pro..
then i reimported it into FL and it worked out pretty well..
also exporting your work as audio-files and reimporting them takes away lotsa cpu-usage and shortens high latency if u use a bunch of plugins simultaneously
cheers