DBlank posted a response for an issue like this, and the solution was along these lines:
create 2 formulas, 1 for the left 6 digits like:
left(totext({table.field},0,""), 6)
and another for the rest of the string like:
mid(totext({table.field},0,""), 7)
place both formulas into 1 text field and mark the second formula as BOLD. when the report runs, only the extra digits will appear bolded.
HTH
I haven't done this myself, but it seemed a fairly elegant solution to this type of issue.