You can create a "contextual link" using this format:
http:// www. amazon.com/ dp/ ASIN/ ?tag=yourAmazonID -20
The ASIN is listed on the Amazon page that describes the product. If it's a book, it will be the ISBN-10 number. Your AmazonID is whatever your Amazon ID is followed by "-20." In the actual url there are no spaces; I had to add them to keep it from being a clickable link.
So when you mention the product in your text capsule, highlight the text you want to use as anchor text and click the link button in the text editor tool bar. Add the url to the url field and click "save" and you should be good to go.
I haven't tried this in a text capsule, but I've done it on another writing site, so I know it works. Just don't know if HubPages will allow it.
But you don't need to do this in an Amazon capsule because products are already associated with your Amazon associates account if you've activated it in the Earnings portion of your account. All you need to do is list the ASIN or ISBN, not an entire URL.
On the other hand, this is supposed to be changing when HubPages pulls Amazon under the umbrella of the HubPages Earnings Program. Amazon earnings will go into HubPages Amazon account, 60% of which will go to you (more about that here - http://hubpages.com/learningcenter/1-3-setting-up-...
So using the contextual link may be the only way you can have Amazon products linked to your person Amazon Associates account.
Hope I haven't overcomplicated my answer.