Postscript underline text

Hi 

I have this postscript script the will underline some of the text

/UnderlineThickness
/UnderlinePosition
/ulshow % string on stack
{
/fontheight { currentfont /FontMatrix get 3 get } bind def
/lineheight { fontheight 1.2 mul } bind def
currentpoint /y exch def /x exch def
dup
show
stringwidth pop dup neg 0 rlineto stroke
x add y moveto
} def
72 720 moveto
/Courier 18 selectfont
(Hello ) show (World ) ulshow (GoodNight ) show (Moon.) ulshow
showpage

I want to put the underline to be in the middle of the text so it looks like it is struck through.

Can you help please? 

Thanks in advance

Rob