Entering custom shipping at checkout time

[Eric Paul <epaul@spellbook.net>]

Is there any easy way to have the user enter a value for the shipping field 
during checkout?  Here's the backstory on why I want to do such a silly 
thing...

My client charges fixed shipping for orders in the US.  For international 
orders (or REALLY HEAVY domestic orders) they want the customer to contact 
a real person at their shop to get a quote on shipping.  My client would 
like a way for international customers to just get a textbox that they type 
the shipping amount they were quoted, and minivend will handle the credit 
card auth's and invoice generation from there.  Yes, I realize there is 
lots of room for abuse here, but my client is willing to look over the 
international orders and weed out the ones that the customer put the wrong 
number in.  They feel this is easier than making every international order 
fax their CC info after they get a quote on the merchandise and 
shipping.  I'm not sure I agree, but hey, gotta please the client...  They 
pay my bills :P

Any easy way of doing this?  Any better way of doing this?

Eric
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Eric Paul
SpellBook Systems
http://www.spellbook.net