There is a suppress property that can be used in combination with conditional formatting formulas to hide these sections. But the probelm is to writing the formula properly. What you'll need to do is use a global variable that is shared between the main report and the subreports. Create a formula in the top of the main report to set it to zero. Then in the subreport's header, set it to 1. For the subreport header in the main report, suppress it when the variable is 1. That way it gets suppressed when the subreport is printing. You're going go have to play around with this a bit because you are basically flipping this variable back and forth between 0 and 1 and only suppressing the header when it is equal to 1. Might get a little tricky keeping track of what the variable is. I suggest printing the variable out in the main report and subreport so you can see how it flips around and confirm that you are setting it correctly.

I cover lots of tips and tricks for using subreports and manipulating data in Chapter 9 of my book Crystal Reports Encyclopedia.