Boxed MText through Leader Command..any way to add thickness to box lines?

Where I work, we put a box around all of our leader notes in on our
road diagrams. Traditionally, we use PLINE to draw the box around the
text, to give it some thickness, and then we link the leader to the
middle of the box. However, I'd prefer to use the box provided
through the "leader" option, except the only problem is that I can't
seem to figure out if it's possible to set a thickness to the box
lines so that it does it automatically when I use leader, and enter my
mtext.
Hope this isn't too confusing...
Along that same note, is there a way to set the line thickness when
using %%U when typing text I want underlined?
Any help would be greatly appreciated....
Dave