Beats and measures, starting with prior pickups

I’m exploring the Beats and Measures timeline view, pretty cool feature
(which I have mimicked previously by constructing a semi-automated label track.)
But my music starts with pickup notes before the first bar line, measure #1.
How can I slide the time line measure numbers to the right, so that #1 corresponds
to the start of the first measure?
(Of course, I can align the first measure with the number 2,
but then all the measures are off by one. Not a big inconvenience,
I DO know how to subtract one in my head, but still.)