16.6 now has the ability to do this. Use the Linear Dimension, select the points you want to dimension then before you place the dimension look to the Options menu (Right hand side) there is a Text override area so you can type -10 if you want. You can also type extra text in here also so -10 2x holes etc length is %v %u where %v is the actual value measured and %u is the units. For leader lines %n works as a another line so this is line 1%nthis is line 2 would give you two lines.
<-------- This is line 1
this is line 2