I want to offer C.O.D. (cash on delivery) as a payment option in my shop but here in Sweden there is a fee for sending packages through C.O.D.

Trouble is, I can't find any way to customize ZenCart to associate a handling fee with specific payment options, so that this fee is added to the sub-total automatically when customers choose C.O.D. in check-out.

Any ideas on how to fix or work around this would be much appreciated!