format the field in crystal so that "0" quantity is blank (suppressed)

The easiest thing to do is to modify the invoice form in SO and put a condition on the quantity control.  If the item on the detail line is a miscellaneous item, then hide the quantity control on the line.  

I would suppress the field on the forms based on item type.

  2  ItemType. . . . . . . . . . .     1 SYY  Item Type . . . . . . . . . . .

                                               Valid:1,3,4,5 Notes:

                                               1=Regular Item, 3=Charge

                                               Item, 4=Comment Item,

                                               5=Miscellaneous Item

                                               {SO7$(15,1)}

What version of the Sage 100 are you using?  Miscellaneous ITEMS (Item type 5) always have a quantity associated, thus qty times unit price = extended price.  Miscellaneous CHARGE (Item type 3) do NOT have a quantity association so the unit price is the extended price.  I tested in 2014 pu4 and charge type misc items do NOT print a quantity on quotes or orders.  

This sounds like it would work for what I am trying to achieve.  Where can I make these updates to suppress the field?