First of all, I just finished digging up my garden and applying compost to it. So how far will you travel to give a massage?
There might be a way to do something like this if you have a ShopSite Pro level store. You would need that level to get the various features that you would need to create your "Coupons", (shopping cart javascript variables, Variable Price product). Note that the contents of the shopping cart are all dumped out by one tag so there is no way you could get the products ordered directly from the table. However, there are javascript variables available in a Pro level store that you could probably use. See http://www.shopsite.com/help/11.0/en-US/sc/pro/cart.variables.html for a list of the variables available. The Per-product Variables would probably be the ones you would find most useful.
Next you would want to create a Variable price product and enable the variable name and variable sku fields.
Then using the information from the javascript Per Product Variables you could substitute the necessary fields, probably name, price and (order number could be used as sku) into the variable product and create an OrderAnywhere type link to put on the receipt. See this forum post for sample code which you could modify http://support.shopsite.com/forums/viewtopic.php?f=1&t=7857 You could also use some of the Extra product fields if necessary since those are available in the javascript variables.
Note that I haven't tried this but it should be possible to do provided you know javascript or can hire someone that does.
Another option might be the Order API (found under Merchandising) and create a script that receives the parameters pass to it about the order and then use that information similar to what I described above. You could either use the OrderAPi too replace the thankyou screen or you could use it to send a separate email to the shopper with the "coupon" Documentation on Order API can be found at http://shopsite.com/help/11.0/en-US/sc/pro/order.api.html