The online button creator has it limitations when it comes to including options for Donations. However, if you manually create the Donation item button code, you can do what you have in mind.
Just to give you an idea of what can be done (as there are various ways), check out the example below. Note, it has few extra features:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Button Example Code</title>
<!-- START META TAG SECTION -->
<meta charset="utf-8">
<meta http-equiv="Content-Type" content="text/html;charset=utf-8">
<meta http-equiv="Content-Language" content="en">
<!-- END META TAG SECTION -->
</head>
<body>
<!-- START SAMPLE CODE SECTION -->
<!-- PARAGRAPH 1 -->
Donation Examples
<br><br>
Using Options.
<br><br>
Widget Fund
<br><br>
<!-- Start of Form -->
<form target="_self" action="https://www.paypal.com/cgi-bin/webscr" method="post">
<!-- If using a Business or Company Logo Graphic, include the "cpp_header_image" variable. -->
<input type="hidden" name="cpp_header_image" value="https://yourwebsite.com/logo.jpg">
<input type="hidden" name="cmd" value="_donations">
<!-- Replace "business" value with your PayPal Email Address or your Merchant Account ID -->
<input type="hidden" name="business" value="your email address">
<input type="hidden" name="item_name">
<input type="hidden" name="item_number" value="WF-1001">
<input type="hidden" name="tax" value="0">
<input type="hidden" name="no_shipping" value="2">
<input type="hidden" name="lc" value="US">
<input type="hidden" name="currency_code" value="USD">
<!-- Replace value with the web page you want the customer to return to after a successful transaction -->
<input type="hidden" name="return" value="http://www.yourwebsite.com/ThankYou.html">
<!-- Replace value with the web page you want the customer to return to after item cancellation -->
<input type="hidden" name="cancel_return" value="http://www.yourwebsite.com/Cancel.html">
<input type="hidden" name="bn" value="PP-DonationsBF:btn_donateCC_LG.gif:NonHosted">
<input type="hidden" name="button_subtype" value="products">
<input type="hidden" name="no_note" value="0">
<input type="hidden" name="cn" value="Add special instructions to the seller:">
<!-- -->
Please enter your donation amount: (Example - 10.00)
<br><br>
<input type="text" name="amount" size="5">
<br><br>
Choose Your Organization:
<select name="item_name">
<option value="Widget Fund Donation - Good Will" selected>Good Will</option>
<option value="Widget Fund Donation - United Way">United Way</option>
<option value="Widget Fund Donation - Boys and Girls Club">Boys and Girls Club</option>
<option value="Widget Fund Donation - West Side Shelter">West Side Shelter</option>
<option value="Widget Fund Donation - Pets and Vets">Pets and Vets</option>
</select>
<br><br>
<input type="hidden" name="on0" value="In Memory Of">In Memory of - Enter Name:
<input type="text" name="os0">
<br><br>
<input type="hidden" name="on1" value="Tax Deductable Email Receipt Requested">Would you like a Tax Deductable Email Receipt?
<INPUT NAME="os1" type="radio" value="Yes" checked>Yes
<INPUT NAME="os1" type="radio" value="No Thanks">No Thanks
<br><br>
<!-- -->
<input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_donateCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>
<!-- End of Form -->
<!-- END BUTTON EXAMPLES -->
<!-- END SAMPLE CODE SECTION -->
<br><br>
<br><br><br><br>
<hr align="left" width="50%" noshade>
<br><br>
NOTES:
<br>
In order to test the code, you must replace the "business" value variable with your PayPal Email Address or your Merchant Account ID.
</body>
</html>
