split line on limit tolerance

Not automatically, you'd have to model this in yourself. Split lines may not be the best thing to do, considering how they play with parent / child relations. One thing to do would be to copy a face or set of faces using the offset or knit surface commands, and then trim the surface. That way you've got the effect of a split line without any of the nasty parent / child problems.

Either that, or make sure this is a normal part of your dimensioning standard. I don't know of a setting to activate this, but it may be controlled by the drawing standard used (ISO, ANSI, whatever). After that, the alternatives are pretty grim. Notes have the abilty to add a dividing line between stacked text.