Just doing this myself.
Just add the following into the product.tpl template where you want it.
<form name=orderform_{%product.index%} method=post action="cart.php?mode=add">
<td align=left width=25%><a href="javascript
: document.orderform_{%product.index%}.submit()">
{include file="buttons/add_to_cart.tpl"}</a>
<input type=hidden name=amount value=1>
<input type=hidden name=mode value=add>
<input type=hidden name=productid value="{$products[product].productid}">
<input type=hidden name=cat value="{$smarty.get.cat}">
<input type=hidden name=page value="{$smarty.get.page}">
</td>
</form>