You can use the Order Anywhere links to send in email that would add the item to the cart. If you want to add both items using the same link you would need to modify the code for the Order Anywhere link to include both itemsl.
Below is an example of how I modified one link to add two products. Note the section "itemnum=30&itemnum=29" Originally the link only had "itemnum-30" and I added the "&itemnum=29" so that product would also be added at the same time.
<a href="http://mydomain.com/cgi-bin/jim/10install/sc/order.cgi?storeid=*126ae8a7cdd25b699011fa&dbname=products&itemnum=30&itemnum=29&function=add"><img src="http://mydomain.com/10store/shopsite-images/en-US/buttons/transparent/blacktext-addtocart.gif" border="0"></a>
If you are using SKU's in your Order Anywhere links you could do something similar only using two skus instead of just the one.
Note that this technique will only work for adding multiple products it can't be used for adding a product and a coupon. This techniques is derived from the multi-add to cart templates described in the help at:
http://www.shopsite.com/help/10.0/en-US ... i-add.html