Matrix - hide null row headers

I have a matrix that has segment, subsegment, and brands.

However, some segments do not have subsegments. For instance,

I need to be able to hide or remove the null header while retaining brand5 and brand6 in Seg B total. I've not been able to find a way to do it nor has any of my coworkers. Is this possible?

Our solution was to effectively make brands 5 & 6 subsegments, but then the formatting ends up being the same as actual subsegments which causes confusion.

Thanks,

Jason