Freight cost coming as +ve on Returns

We have a situation where we apply the Freight Cost at Order Level not at line.  When we create the return the charges are coming as +ve amount instead of -ve amount.   If it's from the line then it will derive the -ve charge.  But in our situation we are creating the charges at header level so when we create the return still the charge coming +ve.  How can we resolve this issue without any customization?

Thanks,

Srini C