The form code I used to customize PayPal's "Buy Now" button, leveraging Harmony's template system.

gistfile1.mustache

<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
   <input type="hidden" name="cmd" value="_xclick">
   <input type="hidden" name="business" value="(your e-mail address)">
   <input type="hidden" name="lc" value="US">
   <input type="hidden" name="item_name" value="Honeyfund: {{ item.title }}">
   <input type="hidden" name="amount" value="{{ item.data.price }}">
   <input type="hidden" name="currency_code" value="USD">
   <input type="hidden" name="button_subtype" value="services">
   <input type="hidden" name="no_note" value="1">
   <input type="hidden" name="no_shipping" value="1">
   <input type="hidden" name="undefined_quantity" value="1">
   <input type="hidden" name="rm" value="1">
   <input type="hidden" name="return" value="http://ren.ai/honeyfund/">
   <input type="hidden" name="cancel_return" value="http://ren.ai/honeyfund/">
   <input type="hidden" name="bn" value="PP-BuyNowBF:btn_buynow_LG.gif:NonHosted">
   <button type="submit"{% if item.data.needed == '0' %} disabled="disabled"{% endif %}>&#x2764; Buy us this gift.</button>
   <img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
</form>