Fortunately, Amazon supports a considerably shorter format url, having the form: http://www.amazon.com/dp/ProductID/?tag=YourAssociateID. This is helpful, but you still need to construct the link, then copy/paste it into your page.
I have created a bookmarklet to help. Drag Make Amazon Link to your bookmarks toolbar to install it, then right-click, select "properties" and change the 'YourAssociateID' text to your actual associate id. That's it!
You can check the link with Amazon's link checker to be sure everything will work correctly.
Here is the bookmarklet code in a more readable format for those who might be interested:
d.writeln('The Amazon.com link is:'+h+'
d.writeln('Your short affiliate link is: