The first option you may consider is using the group label tool. Grouping all labels will also group blocking.
If you choose not to group label all blocking, here is a blocking label work-around for version 7.5.0.
Job Properties > Job Settings > Labels > Labels: Floor > Blocking Panel
Change "Suppress Labels" from No to Yes.
This will suppress all blocking labels. Now when you want one label for all the blocks, select the block. In the Properties Grid > drop-down, choose Label.
Then change this label to Unique > Yes, Suppress Labels > No.
It's clunky, but it involves the fewest number of steps to get back to a single label.