How do I set this up? Is this even do-able?

I charge $3.50 to ship up to 10 lapel pins. I want to charge an additional $1 per lapel pin over 10.

Setting up "shipping" and "shipping2" is the easy part.
<input type="hidden" name="shipping" value="3.50">
<input type="hidden" name="shipping2" value="1.00">
<select name="quantity"> etc. </select>

1.) How do I set it up so shipping2 is applied if quantity is more than 10?

2.) If a client adds a different pin, or 5 pins, I want the cart to apply shipping only once. The way I have set it up, every time you add a different pin to the cart, name="shipping" has to add an additional $3.50, because each pin is on a different form.

3.) If you need to see what I've done, here it is:
http://deletemasonicrega...delete.net/?page_id=588

Am I expecting too much from this kind of shopping cart?

Thanks. Be gentle. I'm new. I have RTHFM :)p and don't see how to do this. I have high hopes, but I don't see a lot of traffic on this forum.

John