My workaround is to do a break/mute at the start of the bar, then towards the end, kick a fill button... Voilå! a 'break/fill'!

Yeah, I know it's not perfect!

It's also fairly easy to turn a fill into a break/fill, as long as you know where in the fill structure you want it. Edit the style, take the fill you want to use, and erase the first two beats or so, erase most of the ACC and just leave bass and drums... voilå!

A REAL break/fill.

If you have MIDI pedals, each of the fills can be addressed individually, so it could be 'on demand' with a bit of work...

I've also used Intro 1 as a break/fill, as it sometimes has a fill to come in. At least the count-in makes for a more drummer like break, as they rarely go totally silent

Customize your styles, and a lot of doors open up. I rarely use the pre-programmed Intros, so they are easily turned into break/fills... with the advantage that you have a different one for each variation (Yamaha and Korg don't do that). Using Intros, you lose the 'instant on' part, but breaks are usually on the 'one', so hitting the Intro switch the bar BEFORE you want the break/fill gets easy enough.

You'd be surprised at what you can make these things do... R-A.com has a plethora of these kinds of tips and tricks...