Rem,
There may be easier ways to do it, but a couple of things come to mind:
1- Have a report element be conditional -- if the attribute is greater than zero, show the number -- otherwise show blank
2- Have a second attribute in your BO that is for report purposes. Have a rule set the second attribute something like this:
BO.TextAttribute=AS_STRING(BO.NumberAttribute)
You may have to use a conditional rule that sets BO.TextAttribute to a blank if BO.NumberAttribute is zero.
Tom