PayPal付款按钮，包含产品详细信息

I am trying to set up a PayPal Payment Button. But my problem is that I configure the product on my site and want to get this configuration after somebody payed with PayPal. So let's say I've got a product called "Product". And this Product has some configurations like:

Size -> Large

Color -> #000000

Now I want to receive this information when someone bought my product.

I made my payment button like this:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
    <input type="hidden" name="business" value="MYEMAIL">
    <input type="hidden" name="cmd" value="_xclick">
    <input type="hidden" name="item_name" value="PRODUCTTITLE">
    <input type="hidden" name="amount" value="SUM">
    <input type="hidden" name="currency_code" value="EUR">
    <input type="hidden" name="shipping" value="3.50">
    <input type="hidden" name="tax" value="19">
    <input id="ppSBtn" type="image" name="submit" border="0"
          src="https://www.paypalobjects.com/webstatic/en_US/i/btn/png/gold-pill-paypalcheckout-26px.png"
          alt="Buy Now">
    <img alt="" border="0" width="1" height="1"
          src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" >

</form>

I tried to achieve this with:

<input type="hidden" name="on0" value="Size Large" />

The problem here is that the "on" parameter is limited to 7 options. But my options vary from 6 to 13.

So I am looking for a way so that my customers can pay their configuration with PayPal but I still get an E-Mail for example with their configuration so I know what they actually bought.

I appreciate any help an thanks in advance!

EDIT: It works with

<textarea name="os0" cols=40 rows=6 style="display: none;">Size: Large, Color: #000</textarea>

But is there a smarter solution?