Customer Collects - Need Collection Date

[chrissie]

Hi. Can anyone help with this one?
I have "Collection in Person" as one of my carriers, obviously (to most people) for customers who live nearby and are easily able to collect their order themselves.
However, (I assume because it's free!) I've got customers living 300 miles away who are selecting this option, even tho it does clearly say that this is for the customer to collect from our office.
I know I could change this by adding all of the counties, and only making this option available to local areas, but it's always possible that someone could be visiting the area and so would be able to collect (this hasn't been the case with anyone who's used it up to now, they just didn't read properley, lol)
What I'd like to do is add a box on there for the customer to put in the date they want to collect, and make this date mandatory. Is that possible.
Thanks in advance to anyone who can solve this one for me