Solution is to use a non-breaking hyphen. Type Command-Shift-hypen
on a Mac to insert one in Word. It shows as long when paragraph and other non-printing character display is enabled, but it is same length as normal hyphen when printed or that feature is turned off.
A bunch of text goes here pushing value to end of line, 100
lb×in-2 continuing here with the line break between negative sign and two.
Add a non-breaking space Ctrl-Shift-space
to force the number to stick with the units too.
A bunch of text goes here pushing value to end of line,
100 lb×in-2 continuing here with the line break between negative sign and two.