2 ways I do fills that might help.
First, set say RS track vol to 0 then in Perf set the vol 100 or whatever. Now hit ReTrig & leave it running. Whenever you want to hear the fill just go into Perf mode & hit the pad. Works great leading up to a pattern change.
Second way that adds variety & allows rearranged steps is this.
Choose individual track lengths. On the fill track, steps 1-16, program your regular trigs or indeed none at all.
Steps 17-32 program your fill/rearranged trigs or whatever. (Program 17-64 for longer transitions).
Now switch track length back 16 & hit play. When you want the fill to sound open up the length!