I'm working on a template tag, but it sounds like our standard (non-wordpress) implementation would work well for you. Check out http://www.wantbutton.com for more details on this:
_w.src = "http://button.wanttt.com/button/script/";
var s = document.getElementsByTagName("script"); s.parentNode.insertBefore(_w, s);
data-style="wb1" data-page_source="PRODUCT" class="wantButton"></a>
If you have the plugin installed and activated you should be able to leave out the script, and if you have a standardized merchant template the included information should be easy to set up.
Let me know at firstname.lastname@example.org if you have any questions. Alternatively, I should be able to get the template tag out there relatively soon.