Use a Promo Box with POST method rather than a simple hyperlink?

Hi, I’d like to use a Promo Box on a page and have the button add a product to my off-site FastSpring order. Below are the instructions from FS, but I can’t get it working with a Promo Box and can’t figure our a different suitable layout element. Is there any way to make the button link work with a POST method rather than a simple URL hyperlink? Any ideas most appreciated.

Sample Code

In these examples, the company ID is julie and the product’s Partial URL Path Name is fontmaker. This order flow utilizes a form with POST method rather than a simple hyperlink.

HTML that may be embedded into an existing web page:

For display as button:

<form method=”POST” action=”http://sites.fastspring.com/julie/product/fontmaker?action=add&#8221; target=”_top”>
<input type=”submit” value=”Add to Order” /></form>
For display as link:

<form method=”POST” action=”http://sites.fastspring.com/julie/product/fontmaker?action=add&#8221; target=”_top”>
<a href=”http://sites.fastspring.com/julie/product/fontmaker?action=adds&#8221; onclick=”this.parentNode.submit();
return false;”>Add to Order</form>

Thanks,
Jill