Yes! On the Style tab for your filter control, uncheck "Allow Select All" and give your filter control a default value. It doesn't have to be a value in the drop-down, you can just make the default value "Select an Office" or something like that...which will make the initial selection blank, and a value will only appear when you select an office.
At this point your box may say "no data" when the default is set, but there's a way around this too. Set the default formatting of the table text to be the same color as the background, but then add conditional formatting to the table that when Office is not empty, the table text is visible. (Note that the table setting for Missing Data won't work here; if you set it to "blank" the "no data" will still appear, so that's why you need this workaround.)
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