Paypal add to cart button with color selection


I am creating a fairly simple clothing site in flash. I have created an add to cart button for paypal and it works perfectly. My questions is…how do I have the buyer specify the color of the garment once they’ve reached the paypal site? In other words, I don’t want a drop down menu on the clothing site. I have the color swatches there and I want the buyer to click “add to cart” and then have the drop down menu appear in paypal. I want them to select their color after leaving the site…To me it just makes the site cleaner and simpler looking.

I have searched and searched and cannot find the anser to this…it seems simple enough to me.

Here’s the code I am using (It is actionscript 2.0):
on (release){
var paypalObj = new Object();
paypalObj[“add”] = 1
paypalObj.cmd = “_cart”; = "[email protected]";
paypalObj.item_name = “Barb Dress”;

paypalObj.item_number = “0544D”;
paypalObj.amount = “$198”;
paypalObj.page_style = “Primary”; //or whichever style you use
paypalObj.no_shipping = “2”;
paypalOBJ.undefined_quantity =“1”
paypalObj.no_note = “1”;
paypalObj.currency_code = “USD”; = “US”; = “PP-ShopCartBF”;
paypalObj.target_winName = “paypal”;
paypalObj.shopping_url = (“”);

var sUrl = '—'
    for (var o in paypalObj)
    sUrl += o + "=" + paypalObj[o] + "&";